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Pigment Volume Concentration and its Role in Color

16 thoughts on “Pigment Volume Concentration and its Role in Color”

  1. Hi Sarah,

    This is an excellent article; such good and thoughtful research! It especially helps me to further understand and differentiate egg tempera from other mediums. I’ll be sure to share it with students and fellow tempera painters. Thanks to you and your collaborators.

    Koo Schadler

    Reply
    • Hi Koo – Thanks so much! Appreciate the positive feedback and so glad that you found the article useful. And definitely please share it with anyone that might benefit. Warm regards, Sarah

      Reply
  2. Hi Sarah,

    It’s Koo again. In thinking about the article, I realize I have some questions. I’m confused what is the ultimately visual affect of PVC on chroma. On the one hand, high PVC means higher chroma. On the other hand high PVC means the irregular surface scatters light and creates a “haze of white, diffused light that appears to blend with the color of the pigment, causing it to seem lighter and often chalky or washed out.” So, does high PVC mean color is ultimately higher in chroma or washed out? Is it initially purer chroma that is subsequently diminished by scattered light? Does the local value of the color in question factor in; i.e. would the chroma of a very light value yellow be impacted differently by PVC than the more or less mid-value blues tested?

    Also, why do the colors you tested appear reddish in the acrylic, wax and oil binders? I know ultramarine has a fair amount of red in it, but I thought cobalt was more neutral..? In other words, what is producing the increased red, and would other colors in those binders also show hints of red or a more pronounced appearance of whatever is that color’s overtone?

    Well, as you know I tend to have questions. Thanks for being available to answer them.

    Koo

    Reply
    • Hi Koo –

      Great questions and I will try to answer them as best I can. In terms of chroma and PVC, you are right that in general higher PVC should mean higher chroma up to the level of CPVC – or Critical Pigment Volume Concentration. It is when crossing that threshold that you begin to have the pigment interacting more and more with voids and the surrounding air, and thus introducing more of the haze from scattered light which will tend to lighten and desaturate the color. And yes, the value and likely even the hue of the colors will make a difference, with lighter colors (especially yellows) being far less impacted. but then, that is true when adding white to these colors as well, no? Not a dissimilar impact. And I can think of some colors that gain in chroma when white is added, or they have lower PVC, as in a glaze, such as Phthalo Blue – which in masstone, when richly pigmented, appears quite blackish but add a touch of white or use in a glaze, and the color is clearly much higher in chroma, becoming almost electric. Some of this is discussed in the article on the Subtleties of Color, which you can find here: https://justpaint.org/the-subtleties-of-color/

      The question of the apparent redness of the colors in oil, wax, and acrylic might be actually easier to see if thought of as the increased blueness of these colors in high PVC systems. That you can clearly see in the color spectra that are shared in the article, where clearly there is a very dramatic jump up in the reflectance of blue wavelengths. In particular Ultramarine Blue seems quite dramatic, jumping some 40% in that area. And while lesser on the Cobalt, the jump is still quite pronounced, and it is this contrast – of the very blue masstones of the high PVC paints, that make the ones where the pigment is fully encased in a binder appear much deeper and “redder”. And if you think of it, this is not unlike the cooling effect we experience when adding white to a color, especially if its Titanium Dioxide, with its strong scattering effect. Also, keep in mind hat we all settled on a specific shade of cobalt and ultramarine blue pigments and there are certainly many, many other shades that could have been chosen. So I do think overall the Cobalt Blue that was chosen is towards the warm side of that pigment, as too the Ultra blue. If you are used to working with a different shade it could definitely make sense that you might experience these shifts less dramatically.

      Hope that helps as always!

      Reply
  3. Great article (I really enjoy reading your articles)! Very informative. Thank you!
    I have a question regarding the volume\percentage of pigment in the tube, before the paint dries. Does watercolors still have almost twice as much pigment?
    The stated volume in oils, is it what Williamsburg uses or is it an average of some artist grade paints from a few manufacturers?
    I am trying to understand how is it that watercolors cost about twice as much as oils.

    Thanks!

    Reply
    • Hi Johan –

      Thanks for the compliment and great questions, which I try to address below.

      It’s a little difficult to go from the ratios in the article to what you might find in a commercial product. The samples were all made at a very basic level of just pigment and binder, as we wanted to isolate how that ratio alone can impact the appearance of colors. However, this simplified approach does not always line up with what you would find in a manufactured product. This would be especially true with watercolors, where at minimum you would also need a humectant and a preservative, and likely other additives to improve dispersion, stability, or performance. So the actual ratios of the pigment you might find in a commercial brand will almost invariably be different from the more basic recipes we each used.

      That said, if you are talking about watercolors once they are dry, or if used in cake form rather than from a tube, then yes, the amount of pigment to binder really will be much greater. This is one of the reasons why watercolors have such a beautiful, pure intensity as well as drying to a matte surface, and also why they remain so vulnerable. On the other hand, if you are trying to calculate the volume percentage of pigment in an actual tube, that is harder to generalize about. The range of percentages that Bruce Mc Evoy gives on his Handprint site feel about right and could serve as rough guide:

      https://www.handprint.com/HP/WCL/pigmt1.html#pigments
      (scroll down to the section on the Proportion of Pigment to Vehicle)

      As for pricing, keep in mind that each medium requires a different amount of labor and work to make a stable paint that can sit on a shelf and still perform many years later. Watercolors, as you might imagine, just require a lot of attention to make well, especially with the pigments needing to be ground so finely and kept from crashing. So comparing pigment percentages alone is not quite a fair way to assess prices between different mediums. After all, if pigment load was the most important element, few things could beat a rich pastel.

      Finally, the percentages given for the oil paint was taken from the actual sample that was made for the testing, which contained only pigment and oil, but overall it was fairly close to what one would expect in any high quality oil paint, with some room for variation depending on processing and the feel the manufacturer is after.

      If interested in learning more about the ratio of pigments in oil, you should also take a look at the following article in Just Paint:

      https://justpaint.org/volume-weight-and-pigment-to-oil-ratios/

      Hope that helps!

      Reply
  4. Thank you very much! It was very helpful and completely answered my questions.

    So from what I see in the different sources, oils tubes actually contain more pigment than watercolors, but due to difference in manufacturing processes, there is a big price difference also.

    In regards to the fine milling in the case of WCs, isn’t it insignificant (price wise) once you start manufacturing and find the proper way to do it so you don’t lose material?
    So is the price gap influenced by the fact that there are more steps in the process of manufacturing WCs? (at least it seems like there are more ingredients for the vehicle)

    Reply
    • I’m not sure you can really state that oil paints will always have more pigment than watercolors. It depends on so many things, and of course how you choose to measure it. It is just a very different type of medium. For example, if instead of a tube of paint you started with a pan watercolor, you would clearly have a system that was more pigmented than oils – HOWEVER, to use it you have to add water, which of course dilutes the paint. So you are faced with that quandary.

      Another thing to consider is that the smaller the pigment particle the more binder you need to wet out the increased surface area. Imagine you start with a 1″ cube of pigment and coat it with gum arabic. Now cut that cube in half. You will need to now coat the new surfaces that are exposed. Now cut in half again, and again, until you reach a very fine powder. With each step you will need to add more and more binder since the surface area keeps increasing, although the volume of the pigment has stayed the same. If you then charted the pigment to binder ratio, what you would see is that as the pigment gets smaller you end up with an increasingly LARGER percentage of binder to pigment.

      The reason this is important is that in oils you can get away with a larger particle size because the paint is tightly bound up in a thick paste and forms a substantial film. But in watercolor, you need to have the particles quite small to stay suspended plus watercolorists prize smooth transparent washes, except in a few cases where granulation is sought after.

      Hope that makes sense.

      Finally as to the cost of milling, even after figuring everything out, you have to mill watercolor pigments longer, with more passes, thus more labor, and you have a much tighter acceptable range of particle size, which further adds to the process. And, while not intimately bound up in the cost of production, watercolors and oils are very different markets. One goes through a lot of oil paints in terms of volume, while a tube of watercolor might last a watercolorist years if not decades before needing another one. Plus even if it dries on the palette it can be reused – so there is never any waste. From that perspective, the more expensive watercolor tube can easily outlast the oils and, besides the initial layout, might cost an artist less in the long run.

      In the end, use the medium that you enjoy and that gives you the results you want. Price should not be the driving factor and they are too different to compare easily.

      Reply
  5. Hello Sarah!
    Could you help me with the CPCV calculation?
    Several authors say it is possible to replace the oil absorption value (which by the way had its ASTM standard canceled without replacement) by the specific area value. Doing the dimensional analysis, the value becomes as g / m². As we are talking about concentration, shouldn’t this value be mass-by-volume?

    Reply
    • Hi Rafael –

      First, let me address your statement about the ASTM Standard being discontinued as that is not the information I have or that is listed on the ASTM Website, where both oil absorption standards (following two different methods) state they are active:

      https://www.astm.org/Standards/D281.htm
      https://www.astm.org/Standards/D1483.htm

      If you have other information please point us to the source as obviously that is important.

      As to your question, while calculating oil absorption by obtaining the calculated surface area of a pigment is doable, in truth we think it is likely not all that easy to obtain as you would need to have information on the specific pigment you are using from that specific manufacturer. The typical calculation, from what I understand, would be to obtain something called the BET-value, named after a trio of researchers that first developed the method. You can read more about it here:

      https://en.wikipedia.org/wiki/BET_theory

      and see a mention to manufacturers turning to the use of BET values in cases where the OA values would be quite high (typically when using pigments with extremely small particle sizes):

      http://www.european-coatings.com/Editorial-archive/Oil-absorption

      Also see ISO 9277:

      https://www.iso.org/standard/44941.html

      Finally, yes, the final calculations would be reported as m2/g.

      In the end, however, OA calculations using one of the older methods can serve “well enough” for a rough estimate and even then because of the variability of the particle sizes of the pigments being used – as well as the variability introduced by the formation of agglomerates – the best one usually gets is a reported range. That said, unless one has a need for something much more rigorous and precise, these ranges still allow you to get in the ballpark and from there one still ends up needing to adjust their milling or mulling to get the stiffness of paste desired.

      Hope that helps!

      Reply
      • Thanks so much Sarah!
        Your answer help me so much!
        It was a mistake, the Brazilian standard (ABNT NBR 5811) for oil absorption determination that was canceled, I apologize for this.
        I will perform and compare some tests with the BET results to the OA results and in the future compare the values of the theorical CPVC obtained with these methods to the Mercury porosimetry.

        Reply
  6. Well amaging research. I have a question what are the solid and liquid particles are used in Matte paint and what is the percentage of that??

    Reply
    • Hello Pranav,
      Matte products are formulated to have maximum amount of pigment and matting solids while still forming a flexible film. The binder is inherently glossy, so the matteness comes from the solids. These solids can include the colored pigment itself and other inert additions like amorphous silica or calcium carbonate. There are many solids that can contribute to a matte sheen.

      Reply

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