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Revisiting Oils Over Acrylics

69 thoughts on “Revisiting Oils Over Acrylics”

  1. Very interesting, but also surprising!

    The fact that adding oil to the paints stopped the cracking could suggest that the paints were under-bound, but I would expect the surfaces using gloss acrylic to be less absorbent than matte or Gesso. What about toothy clear gesso which has a rough surface, was that tested?

    Also interesting that it seemed to only occur in one range of thicknesses. I would expect it to occur in thicker paint films as well, but that’s not what you found.

    Did you try ACM panels as well BTW?

    I’m not sure what else would cause paint films to crack like this on a rigid surface when the layer underneath was not oil that was already drying..

    Reply
    • Hello Richard,
      Thanks for your thoughtful comments. We are certainly intrigued by the underlying mechanism that is causing this cracking!

      You are right to question the absorbency of the different products. That is something we have looked into – cracking happens more on glossy acrylics, which are less absorbent, and less on matte or other absorbent products – which seems counter intuitive. We have looked at clear gessos, Matte Medium, Pastel Ground and found variable results – better than gloss, but still not perfect. In general, matte products seem to crack less which is why we are recommending adding oil when working over these type of products. Even that 5-10% seems to be enough to push applications into the safe zone.

      We have not seen cracking with this phenomenon in thicker applications. That is not to say that thicker applications might not have their own issues in the future. But, with this it seems to be isolated to that specific range between .05mm -.25mm. This range seemed to be the zone regardless of the substrate. We didn’t try ACM, but did work on wood panels and canvas mounted to panel. The laminated cards provide a nonabsorbent, inert surface and seemed to provide consistent results with all the other substrates we tested.

      BTW Scott shared your recent portrait and it is very lovely!
      Take care,
      Greg

      Reply
      • Hi Greg,

        Thanks for the kind words on my portrait 🙂

        I know that acrylic paint films swell and then shrink back when exposed to water. I am wondering if perhaps they are swelling with the oil and the fast expansion and contracting is causing cracking? Adding oil would slow down the drying process and perhaps the resulting stresses from the acrylic expansion?

        Just an idea..

        Reply
        • Hi Richard
          It is an excellent idea. We will be investigating questions like this with our research partners at conservation departments in the US and Europe who have the kind of tools necessary to measure swelling and/or to be able to detect migration of specific compounds from one layer to another.
          Thanks for your thoughts!
          Greg

          Reply
          • Thanks Greg 🙂

            Another quick thought.. Although not sound archival practice, perhaps testing oil paint over acrylic gloss medium that has first had a couple of layers of gloss varnish applied over the acrylic medium? It would be interesting to see if this has any effect or not.

          • So many things to test!! The question then becomes, why is the GAC or gloss medium so important that an additional type of material should be introduced into the structure of the painting.? Varnish is a tricky material to include, as it is resoluble and most natural varnishes tend to yellow and harden with age. Modern varnishes can introduce a whole other group of problems in that some acrylic resins are lipophilic and can soften when wet oils are applied over top. So, those certainly would not work! We will keep looking for appropriate products that may be used for this purpose.
            Take care Richard,
            Greg

  2. Very interesting! I like that time-lapse of the paint drying. Did you try brushing the paint on instead of using a palette knife? Could the striations from a brush lessen the developing paintfilm tensions? I noticed that some of the ridges left from the palette knife developed into cracks on your video (while some cracks just developed where the paint was flat).

    Reply
    • Hello CF
      Thanks for your feedback. Great question!
      Yes, we did test brushing as well as smooth applications. The striations in the brush strokes seem to provide a “weak point” in the application where cracking might be more likely to develop as long as it is within the thickness range mentioned in the article. We have seen some cracking develop along the base of a brush strokes – following the striations of the stroke (This was mostly only observable under the microscope at 10 or 20 times magnification). We saw this with knife applied applications as well, where cracking would follow the base of a ridge or texture in the application.
      Take care,
      Greg

      Reply
    • Hello Sooz,
      Not necessarily. We have seen some cases of lean oil paints crack over Clear Gesso or Matte Mediums that have been applied over acrylic colors. If painting oils over acrylic colors is a necessary part of your practice, we are recommending adding at least 5% oil or medium to the oil paints and then working directly over the acrylic colors. Clear gesso may not help improve outcomes.

      Reply
      • Thank you for this information. Very helpful. It’s not a necessary practice, just felt like a quicker (drying time) step. With this knowledge, I think I’ll finish all future acrylic paintings with acrylic paints and mediums and begin any new oil paintings using oil paint only. This is timely, as I was just getting ready to start a large oil painting over an existing acrylic underpainting, and now will change the plan and finish it in acrylics. Thanks so much.

        Reply
        • Hello Again Sooz,
          You are welcome! That sounds good. Keep in mind, that if you tend to add medium to your oil colors anyway, then you should be fine to work with the modified oils over the acrylic underpainting. It is understandable that you might be reluctant, but please know that any cracking over acrylic color even with lean oil paint, is minimal when it occurs, and in those cases often only visible with magnification. So, oil additions should push things into the safe zone.
          Thanks for your feedback an comments!
          Greg

          Reply
  3. Though I don’t directly paint over acrylic other than acrylic gessoes, I did note cracking over a slightly slick alkyd primer some decades back. (Which I quickly discarded BTW.) The drying cracks seemed much larger, if fewer in number, when used and painted over on non-canvas panels. On canvas the cracks were much smaller and followed the brush strokes and weave of the fabric. The cracks on the canvas were only noted under careful inspection and seemed to some degree to read as a feature of the creative process. As such they didn’t seem very objectionable. However on the smooth panels the cracking effect was judged more visually disruptive. I think the cracks were fewer but larger on the slick panels because the paint had nowhere to hold or be impeded in its shrinkage. The paint film was largely allowed to freely retreated in dimension until it broke into visible cracks. Where as every bump in a canvas weave provided a natural, but smaller break point.

    Marc Kingsland

    Reply
    • Hello Marc,
      Thank you for your feedback. This is very interesting, though it sounds like a different mechanism at work with your cracking. Did your cracks develop upon drying of the oil colors over the ground, or did it take time? One difference is that in our testing, the adhesion of the oil paint or oil ground to the acrylic, even glossy acrylic, is excellent. There was no slipping on the surface or failure in that regard. Could the cracked paint on your surface be chipped right off or were the platelets fully adhered?
      Best,
      Greg

      Reply
      • The cracks appeared within days or weeks. Too much time has passed to be precise as to how quickly the cracks manifested, but basically upon drying. The paint seemed to be fully adhered, but I didn’t attempt to chip it off. However I had little faith in the panel pictures so never offered them for sale. Plus they also seemed in part to be visually pre-damaged.

        Marc.

        Reply
  4. Can I still size a panel or canvas using Gac-100 to prepare for an oil painting, I use an oil ground on top of Gac-100 after 4 days to prepare the surface for oils.

    Reply
    • Hello Martin,
      We have changed our recommendation based on the findings reported in the article. We have seen lean oil paints (directly out of the tube, without the addition of oil or medium) crack over GAC 100 and other glossy acrylic products. For that reason we now recommend preparing canvas or panel with at least 3 coats of acrylic gesso only (without GAC 100), allow that to dry for at least 3 days, then apply the oil ground over that. Oil paints can also be applied directly to the Acrylic Gesso if desired. We have not seen this form of cracking develop over the professional acrylic gessos we have tested.
      Please let us know if you need additional clarification. You can email directly at help@goldenpaints.com
      Best,
      Greg

      Reply
        • Hi Again Marc,
          We tested GAC 400 earlier to see if it improved results under the GAC 100, which it didn’t, but neglected to look at its influence under Gesso. We have the canvas ready to test and should have results end of next week. We will update this communication then AND will review those results on our May 10th Facebook Live event at 2pm.
          Thanks for helping us cover all the bases!
          Greg

          Reply
  5. First I would like to thank you all for your continued research. In this case, I am confused though–the “phenomenon” does not seem to be clearly defined anywhere other than an insinuation that it is the cracking itself. However, this line seems to indicate that the phenomenon is something other than the cracking, “Our testing indicates that if cracking develops in the oil layer because of this phenomenon…” Can you please give a clear description of what the actual phenomenon is (if it is something other than the cracking itself?) Thank you.

    Reply
    • You are welcome, and thanks for your feedback Anthony!
      We may have inadvertently confused the cracking itself with the mechanism that is causing the cracking, and called them both a “phenomenon” at different points in the article. In relation to the quote you provided, we were referring to the mechanism that is causing the cracking. We understand the timing of the cracking, what combination of materials can cause the cracking, what combination seem to resist cracking and some of the parameters around the cracking…but we do not understand why it is happening. We have presented this information, in detail, to a dozen world-class conservation scientists and not one has ever reported on or researched this topic. It is because of this unknown quality that we refer to the mechanism behind that cracking as a phenomenon.
      We look forward to continuing our research and uncovering more about these strange and nuanced materials…and then of course sharing the results with you!
      Thanks again and take care,
      Greg

      Reply
  6. Greg, thank you so much for providing us with the findings of your research. It’s going to take awhile for me to wrap my head around this, because my absolute favorite “primer” to paint on in any medium (gouache, acrylic, or oil) is a couple of coats of Golden Matte Medium! I love that I can see the color of the substrate. I love the way it grabs the paint, that I can wipe right back to the surface, and that it is less absorbent than gesso. I use it in my sketchbooks, on canvas panels, on boards, on rag matboard… I like it so much better than gesso, and hate to say goodbye! I am also a little confused about the distinction between gloss products and matte. It says in the article that gloss acrylic products produced the most cracking, but then it said that a coat of matte medium over the gloss was sometimes worse. Is that due to the extra layer of acrylic, or due to the matte medium? So is it better to use matte medium than gloss medium if choosing one? If I add a bit more alkyd medium to my oil paint, would that resolve the issue for me in any case, and could I then continue using the matte medium as I have been? Many thanks for any clarification you can provide, and also for the upcoming FB Live talk and Q&A.

    Reply
    • Hello Jamie,
      Thank you for your comment/ question. It sounds like you are understanding correctly – Gloss acrylic mediums are causing the worst cracking. Matte Medium and Fluid Matte Medium are less, but there is still the potential for cracking in lean oil layers that are applied over these products. Because the potential is reduced over Matte Medium, we are not recommending against it entirely, but rather simply adding oil or medium to your oil colors to reduce or eliminate the risk. We have found additions of about 5% or more is enough to bring oil applications into the safe zone, especially when working over Matte Medium or acrylic colors. 5% is not much at all, a couple drops of oil to a small nugget of paint.
      We will be sure to reiterate this idea during the FB live, but in the meantime please follow up with any additional questions.
      Best,
      Greg

      Reply
    • Hi Janet,
      Thanks for your question!
      We have not. But, We have had several artists request information on that combination already, so will be testing ASAP. We will share results during our FB live event on our Golden channel on May 10th and will come back in to these comments and update our replies with what we find.
      Take care,
      Greg

      Reply
  7. Thanks, this is concerning. I’ve been following Golden’s recommendations closely and swore by GAC100.

    “We have not found cracking in oil applications over GOLDEN Acrylic Gesso, …. This is also true for most other brands of acrylic gesso we have tested.”

    What about pre-primed canvas and linen (usually acrylic, and oil ones can contain zinc)? I wonder if canvas companies do their own tests like Golden. Should I buy single layer “pre-primed” linen or canvas and apply my own extra Golden gesso layers? I couldn’t be bothered to rinse then dry and gesso raw linen.

    It is nice to paint on clear primed linen. I wonder if extra tooth in rougher linen helps, although that’d probably help adhesion nor cracking, (and what about testing primed textured linen versus poly which is smooth).

    Is there an additive in all acrylic paints that could cause the problem?

    I also wondered if you’ll test paint brush strokes versus draw downs

    Where will I be able to find the link to watch the video afterwards? Thank you for this

    Reply
    • Hello Lej,
      Thank you for your comments. Did you ever see any issue when working oils over your GAC 100? Did you use Oil Ground or Gesso over the GAC?
      Most pre-primed linen or canvas use a universal primer which is typically acrylic. An additional coat or two of Golden gesso or another professional brand should be good to make a nice surface for oil painting and should block oil with a total of 3 coats. Be sure to let the gesso dry for about 3 days before painting over top with oils.
      We have seen some cracking over clear gessos, so please note the recommendation for adding oil to the paints before painting over those surfaces. 10% of a regular drying oil and 5% stand oil or alkyd medium should be good to get you into the safe zone.
      We have not been able to isolate a specific ingredient that seems to cause this issue. our investigation will continue with conservation scientists in the US and Europe to try and learn more about this phenomenon. We will certainly share our results.
      The Facebook video should remain on the site after the event so you can go back and watch it later. It should also be on our Youtube channel.
      Take care,
      Greg

      Reply
  8. Thanks for your research. I still have some panels prepared years ago, using GAC 100 for sizing, over which I applied many, many coats of acrylic gesso admixed with marble dust and talc. (I like an absorbent surface.) After reading this, I’m a bit concerned, but I think I would still take the chance of using such a panel for oils.

    1. I’ve not had any problems so far with such panels.

    2. The years of aging have probably helped.

    3. I tend to apply oil paint thinly.

    4. Your testing doesn’t really replicate the preparation I did.

    But I’ll let you know if the oil paint ever cracks or flakes or hops away from the surface.

    Reply
    • HI Joseph,
      Thank you for your comment. Glad to hear you have not seen any issues so far! We expect many artists are also using oils over acrylic without issue, but just want everyone to know there is this potential when combining these two materials.
      We tested 3-4 coats of gesso over GAC 100 and found the gesso layers seemed to block most of the tendency for cracking in overlaying oil layers. And when it did crack in this situation, it was miniscule or microscopic cracking. If a small amount of oil or medium was added to your oil colors, then it is very likely that cracking would not occur with this preparation. The addition of talc and marble dust to the gesso probably help too.
      In reference to #2, we did not find aging of the acrylic help noticeably. And #3, thin, lean applications is actually where we are seeing the issue. So that is something to look for. Let us know if you come across anything in your older works or if new projects develop cracking upon drying of the oil layers.
      Best,
      Greg

      Reply
  9. Hello Greg,

    I apply very thin layers of Burnt umber directly from the tube on top og GAC100 and haven’t seen any cracking yet. I often ‘oil out’, that is applying a thin oil-layer on top of the dried oil, before applying another layer.

    Might the ‘oiling out’ substitute the adding of oil into the color in application?

    (And thank you very much for this news-letter, this is my first edition and it is already super relevant)

    Best Regards
    Claus

    Reply
    • Hello Claus,
      We are glad you found the article helpful! Thank you for the feed back! It may be that the burnt umber is not as vulnerable to this type of cracking as some other colors. If that is the case, then great. We have tried to ascertain which oil colors are most likely to crack in this situation and why, but have not found the pattern yet. If the burnt umber is drying and not developing cracks as it becomes dry to the touch, then it is likely not to have an issue. The oiling out is fine as a preparation for the next layer, but it shouldn’t have anything to do with preventing this type of cracking. That said, it may support the layer that the oil gets worked into, so the second layer may benefit from the oiling out.
      Curious if there is an alternative to the GAC 100 for you moving forward. What do you like about that product, and can it be replaced by several layers of Gesso?
      Best Regards,
      Greg

      Reply
      • Hello Greg, sorry for this late reply, these forums are new to me.

        I use the GAC 100 for two reason:

        1) This method was introduced to me by the artist Annie Stegg Gerard in a tutorial I bought. She first does a pencil drawing, fixates that with GAC100 and then uses the raw umber as an underpainting (sorry that I wrote: burnt umber previously). Then she goes on to do elaborate oil paintings on top of that. I haven’t written to her about your findings, but she doesn’t report any cracking.

        2) I do an elaborate pencil-drawing on the paper first, and I want to preserve some of that linework in the finished piece. Because of its low viscosity, GAC100 can be applied without smudging the pencil. The smudging could probably be prevented with a layer of spray coating before applying a more viscous protection.
        The glossy surface of the GAC100 also lets me mix pencil into the raw umber, the oil dissolves the pencil line achieving a ‘lost and found’ quality.

        I have uploaded two photos of recent experiments here:

        https://www.dropbox.com/sh/h7dyims0he0qcvv/AABk1xC9LInCYu_HdljfmVSDa?dl=0

        I could use Winsor and Newtons Clear Gesso Base instead of GAC100. Would you recommend that?

        Thanks again

        Reply
        • Hello Claus,
          Thank you for the details of your process. Those are great little paintings!
          If you have not seen any issues to this point, it may be fine to just continue as you are. In general though, we have seen better results over Matte Medium or Clear Gesso than working oils over GAC 100. Are you using the GAC 100 to both size the paper and lock down the pencil? Or do you have Gesso on the paper first, then pencil, then GAC 100?
          If the paper is already Gessoed, then you might try drawing with pencil and then working the oils directly over top without isolating, Or substituting the Matte Medium or Clear Gesso in place of the GAC 100 if it is just locking down the pencil. Your oil layers seem relatively thin, which may be below the threshold for when we are seeing this issue. Also, we have not tested a variety of umbers from different manufacturers, but our umbers do not seem to show a propensity for cracking due to this phenomenon. We will have to report on that later as we get more results.
          Hope this helps.
          Take care,
          Greg

          Reply
  10. Hi Greg, thank you for the awesome content that you produce! I apologise if I am about to repeat a question that has already been asked. I have read the comments, but am still puzzled by the GAC100 issue. I paint on wooden panels, which I first seal with GAC100, before applying gesso. My oils are applied directly over the gesso. Am I correct in concluding that I should rather apply the gesso directly to the panel? Also, if I may add a second component to this question – I have read that sandable gesso should always be applied over a layer of regular gesso. Is this true? In other words, is it your recommendation that a panel be primed with a layer of regular gesso, followed by sandable gesso, followed by oil paint, thus leaving out the GAC100? Your advice would be appreciated!

    Reply
    • Hi Alex,
      Thanks for your question. Yes, we are recommending against GAC 100 or Gloss Medium as a preparatory layer before oil painting. Instead, Gesso can be applied directly to the panel in as many coats as desired, allowed to dry for at least 3 days, and then oils over top of that. The Sandable Hard Gesso can be applied directly to the panel too, but the concern is if the panel is too absorbent, then the Sandable product may crack upon drying. Absorbency of the surface may depend on the type of panel that is being used. Most can take the Sandable Hard Gesso directly when it is applied in thin layers. You should be able to see if there is an issue right away as the SHG dries.
      Hope this helps. Let us know if you have additional questions.
      Greg

      Reply
  11. Hello,Greg

    Thanks for your newest testing , it is very helpful ,and i wonder if you have done any testing for Very Large size oil painting ,Like 2meters * 3meters for Oils Over Acrylics ?

    1# What is your recommendation for large Size oil painting ? Linen Fabric +3 layers Golden Acrylic Gesso (3550 ?) +Alkyd Titanium Oil Ground ?

    2# Alkyd more adhesive than Linseed oil ?

    3# PVA 2 Layers +Alkyd Titanium Oil Ground ,Acrylic Gesso 3layers+ Alkyd Titanium Oil Ground , For Large size Oil painting Adhesion ,Which is better ? PVA or Acrylic Gesso ?

    Thanks !

    Reply
    • Hello Gavin,
      Thanks for your comment. We did not test extra large canvases, but imagine this issue could effect surfaces of any size with the right combination of materials. For a successful outcome, either PVA Size or Acrylic Gesso could serve to prepare the canvas for oil ground. The PVA does not create much build on the surface, so if you want maximum canvas texture, then go with the PVA. If you want to fill the weave some and increase stiffness of the canvas (which may be good on a larger piece) then 3 or more coats of Gesso should be sufficient to block oil and prepare for the oil ground. Adhesion should be equally good for both. Alkyd binder or oil binder both provide good adhesion to a properly prepared surface. Applying Gesso with a trowel can speed the process and create a smoother surface.
      Hope this helps. Best wishes with your work!
      Greg

      Reply
  12. Hi Greg,

    This was very helpful to me as someone who is new to oil painting and just figuring things out. I have a question about whether or not one can paint on vinyl with oil paints or if you should stick with acrylics. I also am trying to figure out how to prep it. I’ll be using vinyl wallpaper as part of a mixed media piece and adhering the wallpaper to a wooden substrate so it has less movement. (I actually just got a whole bunch of vinyl wallpaper samples and am very excited to reuse and recycle them.) What’s the best way to submit this kind of question?

    Thanks!

    Lori

    Reply
    • Hello Lori,
      That is a good question. We have not tested oil paints and mediums on vinyl wallpapers. Adhering the paper to a panel should provide support for the oils as they age, which do become increasingly brittle, but there may be different types of degradation associated with the wallpapers that we do not know about. Acids in the paper can cause yellowing or embrittlement in the paper fibers over time regardless of whether the paper is embedded onto a surface. Also, some vinyls contain plasticizers that can evacuate over time. As these volatile compounds leave the vinyl, they can trapped in the oil layers over top and may disrupt the drying of that film. They may cause the dried oils to become sticky or soft over time. We have seen this with acrylics over vinyl and are only speculating that this might happen with oils, but its a potential. Before going too deep into a body of work with this combination of materials, it may be good to test on a small scale. Also, regarding the topic discussed in the article, if a gel or medium is used to adhere the vinyl to the panel, and the oil paints come in contact with that acrylic product, then that may cause other issues, such as the type of cracking that we have recently discovered. To discuss this issue further please feel free to call 800-959-6543 and ask for Greg in technical support. Or email gwatson@goldenpaints.com.
      Best Regards,
      Greg

      Reply
  13. Hi Greg

    Having read the article and discussion below, I can say I use similar (although not exactly the same) process as Joseph Cannon described above. Right now, I’m about to finish preparation of three panels. In my case it is:
    1. I mount fine textured linen over braced HDF board using acrylic glue.
    2. After a day or two I rub the surface of the linen with pumice stone to get rid of little knots; even though it is extra fine textured linen, I find these little knots annoying.
    3. A layer of Fluid medium matte. After it has dried, some rubbing with pumice stone again. Then another layer of Fluid medium matte.
    4. Two layers of acrylic primer applied with palette knife to fill the weave of linen (which is still slightly present).
    5. Another 3 – 4 layers of acrylic primer applied with brush.

    Sometimes I paint directly with oil paints over this, sometimes I apply oil ground – in this case e.g. Williamsburg Titnaium or Lead ground thinned with turpentine in proportion 5 parts ground to 1,5 parts turpentine. Whether first or second case, I typically wait 3 – 4 weeks before applying oil ground or painting with oils over acrylic primer. As for acrylic primers, I use either Golden Gesso or Lascaux Gesso (first 3 layers) and Lascaux Primer (second 3 layers).

    And for the very first layer or imprimatura I usually use either paint straight from tube or paint mixed with medium made from chalk ground in linseed oil (similar to Velasquez medium by Natural pigments) and in both cases sometimes thinned with small amount of turpentine or spike oil.

    One panel was prepared with 3 layers of WB Titanium oil ground and beneath it, If I remember well, were 4 or 5 layers of Golden Gesso, and beneath the Gesso Fluid medium matte and GAC 100. The oil ground was left to cure for few months. I haven’t observed any cracks in cured oil ground, or succesive paint layers (so far 2 layers applied).

    So, in short; linen mounted on HDF, then sized with Fluid medium matte, then prepared with 5 – 6 layers of acrylic primer and then painting with oils. I guess, I could say the same as above mentioned contributor Joseph Cannon, i.e. „Your testing doesn’t really replicate the preparation I did.“ Well, anyway, I guess I should be fine, what do you think?

    Best regards
    Ivan

    Reply
    • Hello Ivan,
      Thanks for describing your preparation in such detail! It sounds like you are applying enough Gesso layers to block any effects that might come from the GAC 100 or Fluid Matte Medium. And if you are adding some medium to your initial layer/imprimatura, then that would provide even more protection from experiencing this issue. In the future if you can remove the GAC or FMM from your preparation, then there should be no concern for potential cracking in the oil layer especially when you are using lean oil paint. Let us know how it all goes and keep in touch!
      Take care,
      Greg

      Reply
      • Hello Greg
        Thank you for feedback.
        As for your recommendation about removing GAC or FMM as a possible practice in the future; I’ve never tried applying acrylic primer directly over raw linen, but I think it could be somewhat… more problematic for me. You see, raw linen is of course absorbent surface. GAC 100 and FMM can size the surface, thus making it almost non-absorbent. Since these are basically only fluids and Gesso contains certain level of solids, I guess it could be difficult to brush the Gesso out evenly as it would dry too fast. The thinning with water might be necessary. Also, I wonder if dried Gesso could be rubbed with pumice stone (to remove little knots) in the same way as dried FMM. I don’t know. Maybe I’ll try it.

        Also I’ve been thinking about the recommendation in the article to wait at least 3 days after applying acrylic dispersion or Gesso before painting with oils over it. Of course „at least 3 days“ means 3 and more, but I wonder if it shouldn’t be at least 4-5 days for one layer of Gesso. That is, in case of 4 layers at least 3 weeks. Maybe 3 days are just not enough for all residual moisture in acrylic primer to evaporate and this could be part of problem?

        One recommendation in the article is to size with PVA size. I’ve never tried it, what I can readily buy here (that „here“ refers to central Europe) is Gamblin PVA size. I suppose you tested PVA size (whether Gamblin or something comparable), can you tell me, how does it compare to GAC 100 or FMM? For example:
        1. In terms of drying speed, leveling, brushability,
        2. Will it dry to surface of similar hardness? One time I tried vinyl acetate ethylene size and even when it was dried it felt slightly sticky to the touch.
        3. Is it possible to sand dried PVA size or rub with pumice stone as it is possible with GAC or FMM?
        4. Do acrylic primers adhere well onto PVA size?

        Best regards
        Ivan

        Reply
        • HI Ivan,
          I like applying Gesso directly onto medium weave linen with a trowel. I use a plastic trowel with softened corners and knife the Gesso smooth. Sometimes if there is a knot, the knife will skip, creating a little chatter, but those can be removed by cleaning off the blade and skimming perpendicular. 3-4 coats like that can give a smooth surface without raised fibers from the fabric. If you wanted to sand off any nubs between coats, that would be fine, but it may scuff back into the surface which would then need to be coated with additional product to block oil. Using a blade to apply Gesso also helps to get the product onto the surface fast, removing any issues with fast drying.

          We recommend 3 days dry time because that is how long it takes for the vast majority of water to evacuate the product. We have applied oil ground over acrylic products after different dry times including several months all the way to the same day, and have not seen noticeable differences in performance. For this testing, we used many surfaces with gloss acrylic that were cured for years and they produced same type of results as working oils over fresh gloss products.

          As for PVA. It was the Gamblin product we tested, though we did not test it under Gesso as a size prior to the gesso layers. It is very thin and water like. It dries at a similar rate to water. It soaks into the fabric and does not create much of a build. But, it may stiffen the knots on your linen enough that you can then come over to sand the nubs from the surface. From our limited testing, it does appear that acrylic gesso adheres to PVA sized canvas.

          We hope this helps!
          Take care,
          Greg

          Reply
  14. Thanks for the useful information. Can you tell me if this study applies to water-soluble oils? I prep my canvas with 2 or 3 coats of acrylic gesso, and do the underpainting in acrylic washes. I then work in water-soluble oils, starting with paint that has been thinned with linseed oil or a ‘painting medium’, and gradually build up slightly thicker layers – but never impasto. I’m just curious if you tested water-soluble oil paints. Thanks again!

    Reply
    • Hello Adrian,
      Thank you for your comment. We have tested some water-miscible oils since publishing this article and have seen good results. We only have 2 brands in house with limited colors, but none of the colors showed signs of cracking over gloss acrylic medium, which is worst case scenario. There should be much less likelihood of a problem over acrylic colors, AND the fact you are adding oil to the initial layers, should put you into the safe zone. If you have not seen any issues, then your combination may be good to go.
      Hope that helps!
      Greg

      Reply
  15. I love Justpaint! I have never seen any comments on Michael Harding’s Non-absorbent Acrylic Primer. I usually use 2 layers over a commercially primed canvas. I like that my colors don’t sink in and remain vibrant. I use to have to do some oiling out. The oil paint takes longer to dry or so it seems to me. Harding claims there is enough tooth for the paint to adhere to. What do you think? Does Golden have a similar product? Best, Mark

    Reply
    • Hello Mark,
      Thanks for your comment. We have not tested that product yet. It seems very Gesso-like. As mentioned in the article, we have not seen issues with Gesso or Molding Paste. It seems the more solids in the form or pigments, fillers and calcium carbonate that are in a product, the better they perform in regards to this phenomenon. In general, if you are not seeing issues with your current combination of materials, then it may be totally fine. Moving forward, we will have to take a look at that and may do a follow up article with some of the suggestions we are receiving in the comments etc.
      Best Wishes,
      Greg

      Reply
  16. Hi Greg!
    I have a question about how one would approach “clear” gesso/ground based on these new recommendations. Recently my paintings involve applying two layers of gac 100 onto canvas or linen (for SID protection), followed by two layers of fluid matte medium, so that the color of the natural canvas shows through. I then apply oil paint over this layer.
    According to these new tests, what would you suggest for a clear ground that results in minimal cracking? Should I avoid gac 100 entirely, even if its applied underneath the matte medium? Does matte medium itself provide some protection against support induced discoloration?
    I’ve also heard people use PVA size on canvas as a clear ground, but I’m worried about oil strikethrough and the oils eventually damaging the canvas.
    Thanks!
    Audrey

    Reply
    • Hi Audrey,
      Thank you for your question. The first step to avoiding this issue is to remove the GAC 100 from your process. While this may slightly change the way your initial layer of Fluid Matte Medium applies to the surface, it will take the gloss acrylic out of the system, which is a step in the right direction. Three coats of Fluid Matte Medium should block oil penetration into the fabric (two coats actually block, but might apply another just to be sure). Because we have seen cracking over Fluid Matte Medium, we still recommend adding some oil or medium to your colors. 5% stand oil or alkyd medium or 10% linseed oil seems to be enough to mitigate issues over gloss acrylic in our testing. Do you tend to add any medium to your paints?
      We have not seen any cracking over PVA Size, but it can allow strike through with oily or slow dry colors. Three coats should be good in most cases.
      We hope this helps!
      Greg

      Reply
      • This is very helpful, thank you! I do usually add medium to my paints – if I understand correctly, is it better to use a fat medium rather than a more neutral or lean medium (like a 50/50 mix of linseed oil and mineral spirits?)

        Reply
        • Hi Audrey,
          You are welcome! It depends what kind of acrylic product you are painting over. Do you work in oils directly over Gesso or do you use an acrylic underpainting, clear gesso or other type of acrylic product? We are recommending removing any type of glossy medium or gel from the painting.
          Over Gesso, simply do whatever you want. We found no way to create this type of cracking over Gesso. Over most other acrylic products we are recommending oil additions. We tested oils without solvent and an alkyd medium that has about 50% solvent. We did not test 50/50 linseed and mineral spirits. But a couple things come to mind- solvent evaporates out of the layer which means if one uses 50/50 solvent to oil, then it would require twice as much medium to get to the ratio we found provides benefit. Also, because the solvent evaporates, it will leave a thinner film, so may not reach the thickness threshold where the cracking begins to appear.
          Have you ever seen cracking in your initial oil layers with your current technique? If not, then you may be fine to continue as you are…Let us know.
          Best,
          Greg

          Reply
  17. If one is underpainting with acrylics, is it better to use your So Flat (or mix regular acrylics with matte medium) instead of using a glossier acrylic?

    Reply
    • Hi Lori,
      We found no cracking in oil layers over SoFlat. But, because they are absorbent, the oil from the application can wick into the SoFlat and leave an oil halo around the oil paint. This is not an issue if you are covering the whole surface, but it might still be good to add a small amount of oil to compensate for the absorbency of the SoFlat. Natural fiber supports should still be prepared with 3 coats of Acrylic Gesso before using SoFlat for underpainting oils. We did not test different levels of Matte Medium into regular acrylic colors to see if there was improved performance. We found that both had the capacity to cause cracking, so recommend adding 5-10% oil or medium to any oil colors applied over either or both of those acrylic products.
      We hope this helps!
      Greg

      Reply
  18. Hello ,Greg

    I have an issue to need to be confirm , Using Acrylic Gesso ,is it Brush better than blade/trowel ? i think it is better ,Cause when brush after 3 coats you still can see the texture/fiber of the linen weave / Knots , after Acrylic Gesso 3 coats ,you can use blade/trowel apply one or two coats of oil ground to make the surface plain/flat . this will better for oil adhesion ?

    Brush the Acrylic Gesso will have more texture/ Knots on Linen Canvas , it will create more good adhesion to Oil , Am i right ?

    i do not care the surface plain/ evenness/smooth ,cause i do not draw old classic or Hyperrealism . I only care to create the maximum adhesion of oil over Acrylic . Any guidelines to create Maximum adhesion ?

    and one more more thing need help ,i am in China ,there are Golden Acrylic Gesso for sell here ,But i am afraid it may produced years ago , May i know when is the expiration date for Acrylic Gesso ? And also for Golden Oil colors what is the expiry date ?

    Many Thanks !

    Reply
    • Hi Gavin,
      Thank you for your question. Brushing the gesso is a fine way to go. We have not seen a difference in the performance either way in terms of adhesion, but having a little more texture to apply the Oil Ground should deposit a slightly thicker layer and, as you mention, it is possible to use a blade with the Oil Ground to get a nice smooth application if desired. Our Gesso product does not have a shelf life. But, it can separate a clear liquid on the top after sitting for a while. Simply shake and/or stir that back in before use and should be fine!
      Hope this helps.
      Greg

      Reply
  19. Hi Greg, The cracking issue of oil paints over acrylic mediums such as the GAC Product Line recently came to my attention and enjoyed the FB presentation on this. As a gold leaf gilding teacher I often have conversations with students who, as oil painters, often wish to paint over gold or other metal leaf, some which may tarnish in time. The conventional wisdom in very recent years has been to apply your msa varnish over leaf that has been gilded on either canvas or a panel. The msa protects the leaf, especially the tarnishable ones. To protect the varnish the idea is to apply GAC 200 over the varnished leaf if on a panel and a 50/50 mix of the GAC 200/500 if on a canvas. With the proper drying time this would allow painting with either oils or acrylics with the GAC acting as an isolating coat for overall protection of the leaf during future cleanings.

    However, now with the evidence of cracking of oil paint over acrylics I am wondering what isolating coat you might now recommend or is the research into this still too early to tell? Do you feel the added 5-10% of oil to the oil paint would be enough to go into the ‘safezone’ that you mentioned? And if so, would the added oil need to take place throughout the entire process of the painting in all its layers?

    Thank you for helping to address these issues Greg, a very interesting and valuable Blog you have here!

    ~ Charles

    Reply
    • Hello Charles,

      Thank you for your comment and questions! There are certain techniques like the one you describe that make it difficult to avoid using oils over gloss acrylic mediums. If there was no alternative but to work over these products, then adding medium or oil to the paint is our best suggestion. If the initial layer of oil had the 5-10% additions, then yes, that amount or more should be used in subsequent layers to maintain the traditional fat over lean rule. Keep in mind, that not all oil colors display a propensity for this type of cracking, so the oil addition is a precautionary measure. It can be mentioned to your students that if they have not seen any issues with this combination of materials in the past with the oils they use, then its likely they may not see this issue moving forward. As an extra step, Acrylic Gesso can be applied over the GAC in the areas where oil paint will be. We found that 3-4 coats blocked this cracking tendency even in worst case scenarios. So if the texture and thickness would not be an issue, then that should help prevent the possibility of cracking, especially if folks want to use lean paint.

      Alternatively, the areas where paint will be applied to the surface can be left ungilded. With just Acrylic Gesso or another appropriate ground applied, and then the oils can overlap the gilding slightly.

      While it does not seem to be part of your proposed technique, I just wanted to remind you that we do not recommend painting with oils over the MSA either, as we have seen the varnish soften when oils are applied over top and cause drying defects in the oils. Here is another article that describes that issue: https://justpaint.org/why-oil-painting-over-msa-or-archival-varnish-is-not-recommended/

      We hope this helps Charles. You can follow up with any more questions at gwatson@goldenpaints.com

      Best wishes,
      Greg

      Reply

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