MITRA Forum Question Details

First, keep in mind that you are venturing into an area that does not have a clear definite consensus around best practices, so you will likely get some range of recommendations, but we are happy to at least share our thoughts. And to be clear, while I reference Golden products, other acrylic brands likely have ones that are similar. 

Based on our own testing, as well as the increasing number of problems conservators have been encountering with thickly applied oils, we think using oil paint in that way is fraught with risks and problems. It is simply not a medium well suited for types of textures that go far beyond what was ever implied by the term 'impasto' as understood in the past. This is particularly true if using paints based on oils other than linseed and walnut, or without the use of lead white which greatly aids in stabalizing oil paints over time.

So, given all that, we think oil paint over thickly applied acrylic pastes and mediums is a reasonable alternative and probably with less risks overall. But to keep those risks to a minimum we would suggest some basic guidelines:

-  paint on an inflexible support if at all possible

-  use molding pastes rather than gels as they will provide more absorbency and tooth for better adhesion. You might also try applying a layer of acrylic ground, aka acrylic gesso, on top, as a way to increase adhesion even further and supply a white ground to paint over.

- allow any applications to dry completely. A very thickly applied acrylic paste could take a couple weeks to even a month, depending on application and environmental conditions, to be fully dry,  So wait as long as possible. Patience is a virtue. here

- multiple thin layers will dry faster than one thick one

- avoid soft or spongy versions, such as Golden's Ligtht Molding Past. 

- avoid creating Hershey-Kiss type of dollops that end in thin, very flexible tails that bend easily.

We hope that helps. And while we think these things will lower the risks, it doesn't eliminate them altogether. Whenever artists push boundaries and the limits of their materials, they are pushing into unknown territory with potentially unknown issues that might not crop up for decades.

Hi -

Lead White produces the most durable and flexible oil paint film and indirectly helps to contribute those properties to a certain extent to the rest of the painting. How and why is more complicated than I can go into here but you can easily research those topics as they have been written about extensively. In the US Flake White is simply another name for Lead White, so you can use paints labeled either way. Titanium White is certainly prevalent and many people who are concerned about the toxicity of lead prefer to use it. We would recommend avoiding Zinc White, or Titanium Whites that contain zinc, thickly or in the lower layers of a painting. For more information concerning zinc oxide you can read the following articles from our Just Paint, which try not to be brand specific and are about zinc oxide in general:

https://www.justpaint.org/zinc-oxide-warnings-cautions-and-best-practices/

https://www.justpaint.org/zinc-oxide-reviewing-the-research/

As for a brand of lead white to try, that is a very personal choice. Utrecht, Natural Pigments, Williamsburg, Michael Harding, Blockx, Maimeri, Old Holland, among others, all produce versions of this. Which one meets your needs is something you will need to explore.

I would still want to add that lead white, on its own, is not a cure-all to the issues of very thick oil paint, but in general lead white in linseed oil will have fewer problems than other possible combinations. But still best to keep oil paint films thin to moderate in thickness.

Yes, avoid light Molding Paste as it is too spongy. Hard and Regular Molding paste would be preferred, and yes you can thin these with water to get them to flow more easily. It will not compromise its hardness, simply will mean that layers would be thinner and shrink more while drying.