I have seen where some manufacturers do give the OK to mixing OMS with their Alkyd Mediums. What if one wished to add a Drying Oil such as Linseed or Walnut oil mixed with an Alkyd Medium to moderate the drying time? Of course, being sure to follow Fat over Lean rules by adding the same amount or slightly more drying oil in the mixture to each subsequent layer.If it is OK to do so, is there a safe maximum amount of drying oil that could be added to most alkyd mediums?For the moderators who also work for a specific brand of art materials, what would be a safe amount of drying oil to add to your various Alkyd mediums?Would it be best to stick to a specific ratio mixture of the drying oil with a chosen Alkyd medium to be used throughout the painting, or should slightly more oil be added to the mixture for each new layer, not exceeding any recommended maximum drying oil to Alkyd ratio?If the answer is no to mixing drying oils with Alkyd mediums, what is the reason for not doing so?
I am looking for a general guideline if that is possible to give a maximum ratio of oil to Alkyd medium that would generally be safe to use with most Alkyd mediums, even if it was a very low percentage. It doesn’t take much Walnut oil for example to slow the drying rate quite a bit with some paints. I realize that all Alkyd mediums are not the same and that some makers might recommend not adding any drying oil to their Alkyd mediums, so it should not be done with those products. Additionally, a maximum recommended amount of medium for one brand may not work for another brand that doesn’t give any ratio recommendations, which means an all-inclusive answer may be impossible to provide, but I was very interested in seeing what you folks had to say about this.
Thank you for taking the time to post a response. Your comments have been helpful in reinforcing what I already thought about the process.
I cannot think of a technical reason that you cannot add drying oil to these medium. It will, of course, slow down the drying rate. Additional drying oil will also increase yellowing but only if the total of the mixed medium is excessive. Contrary to popular belief, alkyd mediums yellow. You only have to look at the brown junk that accumulates around the cap of old bottles of Liquin, etc. Finally, overly oil paint films are spongy and make poor films. Alkyd mediums are probably superior in that case. Finally, it is said that alkyd paints, and I have to assume mediums, are slightly more brittle (or at least less flexible, than those made from linseed oil. Certainly, a thick unpigmented alkyd makes a better film than does a thick unpigmented linseed oil film. In this instance, the seeming defect becomes a virtue.
There is no real maximum ratio of drying oil to alkyd medium other than the issues related to the above points. People have used linseed oil or stand oil thinned with a solvent as a medium for centuries and there is no reason why this should suddenly become verboten. If it were, that would mean that one should not add an alkyd medium to linseed oil paint to begin with.
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