I’m sure this has been addressed here ad nauseum and don’t wish to create more work for anyone. Can you please direct me to a resource that can educate me on the use of mediums and whether mediums that speed drying are considered fat?
I paint in layers without solvents and am currently using Gamblin’s Solvent-Free Gel and Medium, both of which contain safflower oil and alkyd resin. These mediums speed drying somewhat over using the paint neat.
I have read two conflicting viewpoints over whether the addition of mediums increases fatness. One opinion is that the addition of any extra oil medium, regardless of whether it speeds drying time, increases fatness. The opposing viewpoint is that any medium that speeds drying has also increased leanness.
I’m not sure how to think of this.
Finally, does painting “same over same,” as one might do when applying paint from the same brand without adding any mediums or other additives, violate the fat-over-lean rule?
Thank you!
Thank you for clarifying this for me and making it easy for me to understand!
Does painting “same over same,” as one might do when applying paint from the same brand without adding any mediums or other additives, violate the fat-over-lean rule?
Ah, so there’s really no way of knowing whether we’re ever painting fat over lean.
The addition of any oil painting medium that does not contain solid particles, such as pigments or extender pigments (fillers), adds to the “fat” of oil paint.
The best way to think about fat over lean is the pigment volume concentration (PVC), which is the volume of pigments and extender pigments compared to the total volume of the dried paint. Adding oil and resins, such as alkyds, decreases the pigment volume in relation to the total volume of the paint—thus increasing “fat”. Solvents do not lower the PVC, because they are volatile and evaporate during drying. Adding pigments or extender pigments increases the PVC; descreasing “fat” or making the paint “lean”.
Each pigment differs in the amount of oil required to prepare as oil paint, so there are “fat” colors and “lean” ones. The apparent oiliness or dryness of the paint straight from the tube doesn’t necessary indicate the proportion of vehicle to paint, either- some lean colors shed a lot of oil in storage, while fat ones may look dry and have no loose oil if stearates have been added to achieve a more workable paste.
I wouldn’t agree that there is no way if knowing; some colors are considered more “fat” or “lean” and this information has been taught and published over many years. If the artist intends to restrict the use of mediums and rely solely on the received condition of the paint for all applications, a general understanding of the nature of each color, or at least pigment category, is an advantage. Also, if colors are being intermixed, the initial paint compositions are quickly altered and it becomes less practical and useful to hyper-focus on this “rule”.
Edit: Also, Mr. O’Hanlon’s PVC description is a better basis for objective comparison. While manufacturers will not disclose proprietary formulas, I would expect most will be open about comparing colors within their product lines according to this term.
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