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Question asked 2019-11-25 17:42:53 ...
Most recent comment 2020-01-11 22:50:11
Can retouch varnish be diluted to make it less shiny, and if so, with what?
Answers and Comments
Which solvent to use depends on the brand and what the carrier solvent is. Retouch damar can be diluted with pure gum spirits of turpentine. Some synthetic retouch can be thinned with odorless mineral spirits. That said, most factory-prepared retouch is intended for use at package strength and may not unify surface sheen to a satisfactory appearance if further reduced. Also, because retouch is generally applied to pictures that are still drying, it's essential to verify that the paint film is not at all soluble before applying any top-coat, especially one diluted with a strong solvent.
Keep in mind that I am a studio artist, not a conservation expert, and I didn't participate in creating the MITRA resources documents. I can tell you from experiece that it's a lot easier to control surface sheen by applying matte varnish over gloss than the other way around. It's probably unlikely that W&N will disclose what specific resins are used in their varnish, so you should probably plan to test a few products, with focus on ones that use the same carrier solvent. I don't see any problem with adding a cold wax matting agent to retouch varnish, but layering on top of such a mixture could be problematic, if you plan on top-coating with a final varnish layer. Also, remember that while picture varnish can be considered by the artist as an integral part of the final pictorial effect, there's a chance that your original varnish might be removed, and your desired matte finish lost with it. Many artists just use matte varnish to solve tricky lighting issues and would not necessarily care if a gloss top coat were later used, but it sounds like you really want these pictures to be viewed with a matte finish. It seems to me that it would be a good idea to document this preference in some way, for the benefit of collectors.
This is a big subject, but what you mention is true.
However, this procedure works best when the high molecular weight coating (or
even a similarly MW, gloss coating) is not soluble in the same solvents as the
upper-most varnish. For instance, apply a xylene soluble b-72 varnish and then
apply a regal-rez or other less polar varnish on top of that layer. The 2nd
coating can be a matte or satin varnish. The essence here is that the topmost
varnish does not overly bite into the preliminary, or saturating varnish. If
you have the capability of spray application, the necessity of differing solubilities
is greatly lessened.
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