I have a student who applied ten, thin layers of Lascaux spray varnish on an egg tempera painting; then, after it had sat for a few weeks, applied a layer of Gamblin wax medium on top. The wax medium felt “sticky” as she applied it so she ended up having to rub it fairly vigorously. When she lifted her rag, there were traces of pigment on it. Ten layers of Lascaux, even thinnly applied, should be enough to fully seal the tempera. It might seem like the solvent in the wax medium dissovled in part the Lascuax, but my understanding is that Lascaux’s solvent is alcohol, whereas the wax medium’s solvent is OMS. Am I correct in that? Any thoughts on what might be going on?
Thanks, Koo Schadler
Hi Brian,
I understand that B-72 is soluble in a variety of solvents, but are you saying that mineral spirits (in the wax medium) might affect B-72 as well?
As you know, I’ve isolated with shellac for many years, followed by a mineral spirit soluble, wax medium on top, without the wax medium layer affecting the underlying shellac. I thought the same would be for B-72, given that it is not mineral spirit soluble, but you’re saying that it might not be? If so, are there any substances that can be applied over B-72 without softening it?
Thanks for your quick response.
Koo
Got it. Thanks, Brian.
Sorry to hear this.
As I understand it, Lascaux is B-72, which is soluble in ethanol and aromatic solvents like xylene. This fact is probably the problem. It is not that importat which of these the resin was delivered in, it remains soluble in both. When one writes “soluble” we mean that, the solvent will put the material into solution. That does not mean that closely related solvents will have no effect if strongly rubbed on the surface. For instance, in conservation we often use PVA solutions that are soluble in ethanol and toluene but not readily in xylene. However, a rag soaked with xylene will disturb a PVA coating. OMS, vigorously applied to a surface that has an application of a xylene-soluble resin coating will likely disturb that coating, especially if it is thinly applied.
Shellac is not soluble in xylene and certainly not in OMS. I am suggesting that strongly rubbing a very thin coat of B-72 with a material containing OMS might disturb the varnish to a small degree. Additionally the OMS containing wax paste can act as a poultice, slowing down evaporation to some extent as well, and extending solvent contact time.
The issue here is the rubbing less than the solubilities. A normal application of either of these materials over each other would have no effect. Vigorous rubbing is the issue.
In conservation we often have to apply a coating over our inpainting that could bite in the lower layer if brushed. In these instances, we have to spray the varnish. This is not applicable to the wax.
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