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Subject: Varnish absorption

Varnish absorption

From: Keith Bakker <keithbakker<-at->
Date: Tuesday, April 3, 2012
Dzenan Sehic <dzennan [at] gmx__net> writes

>I am working on painting from XIX century (said the owner, but I do
>not think so) and I have reached the point where I have to varnish
>the painting in order to do my retouching but I have a problem that
>I have never had before. The absorption of the varnish is completely
>abnormal and randomly distributed. ...
>
>...
>    Revarnished, using Regalrez in white spirit, 15-17% solution,
>    applied with an air spray system
>
>But here is when the problem began. The absorption is completely
>abnormal and there are even glossy spots that should not be there;
>Regalrez is a resin that gives us satin effects.

I had the exact same problem while conserving a genuine and
untouched 19th century varnish on painted wood.

I strongly suspect that it *is* the Regalrez that is at fault. I
can't explain why it would work well one one surface and not another
but that is also exactly what happened when I used it. It worked
well on one surface that had received a different treatment but
performed very poorly on a second surface.

My first suggestion is don't use Regalrez as there are other better
handling materials that meet the same solubility requirements.

Second, if you do, reduce your mixture to a 4% to 5% solution,
absolutely no higher, and apply more coats as necessary.

Third, far from ideal, but you can increase your psi to 40-50 psi
and use an airbrush with a very fine tip. This will reduce the
glossiness of the glossy areas and bring them closer in appearance
to the more matte areas.

Finally once the varnish has dried you can judiciously apply a polar
solvent to the varnish to further reduce the glossiness of the
glossy areas. I'm not sure what you're looking for here but I highly
doubt you will be able to achieve a uniformly glossy appearance
similar to that of dammar.

Having had to do all this to achieve a relatively uniform and
relatively matte appearance, I still recommend not using Regalrez
when we encounter this particular problem.

Please feel free to contact me if you would like to discuss any of
the details further.

Keith Bakker


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                  Conservation DistList Instance 25:45
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Received on Tuesday, 3 April, 2012

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