Wednesday, September 25, 2019

The Great Painting Cull, Part 2

One of the three products I've used for covering up old paintings.

Yes, you can paint over old paintings—so long as you take certain precautions.

You may recall that I recently wrote about going through my inventory of old paintings and culling them.  I very briefly mentioned what I do with the culls.  I thought I'd take a moment now to offer a little more detail.

Warning #1:  This applies only to oil paintings made on a rigid support.  I don't recommend the approach for acrylic paintings or paintings made on stretched canvas.

Warning #2:  As much as I try to use nothing but archival materials in my painting process, I have no proof that the stain-blockers I use are archival.  Based on my layman's knowledge of chemistry and physics, I believe the end product will stand the test of time.  (Honor's Chemistry was as far as I got in college, but I did win the Georgia Tech Distinguished Math and Science Scholar awards in high school.  And I've read a lot of popular science books since then.  All that said, I do welcome feedback from conservators!)  I recommend you proceed cautiously and don't paint any masterpieces.

Here are the steps:

1. I sort the culls into two piles:  One of paintings with significant impasto and texture, and another with little or none.   The pile with lots of texture I scarify with a knife and toss in the trash; these paintings will be too much trouble to sand down.  The second pile will take less work, so these I keep.

2. Any varnish on the paintings first must be removed.  I take the appropriate solvent and dampen a lint-free sock with it.  I rub the surface with the sock until all the varnish is gone.   By the way, after varnishing a painting, I always write on the back of the panel what type and brand of varnish I used.  This information will be useful in the future if you (or a conservator) need to remove the varnish.  Not all varnishes use the same solvent.  Damar varnish, for example, must be removed with turpentine.  I use Gamblin's Gamvar, which must be removed with mineral spirits.  I use Gamsol.

Putty knife and sanding block -- perfect for removing texture.

3. Once the solvent has evaporated, I use a putty knife to scrape off as much of the obvious texture as I can.  Then, using a sanding block, I give the surface a light sanding.  I don't sand all the texture off; just the texture that would look odd poking up through the new paint.  Sometimes you don't want the texture of a tree showing in the over-painted sky.




4. Next, I brush on one coat of stain-blocker with a 2" gesso brush.  My choices for stain-blocker:  Winsor & Newton's Oil Primer, Zinsser's B-I-N (a shellac-based product suspended in ethanol) or KILZ (the oil-based version, not the latex one.)   I do not use a latex or acrylic stain-blocker as this layer will not adhere properly to the layer of old oil paint and will delaminate.  Also, I have been tempted to use two coats to completely obliterate the old painting, but I've found that one layer is really sufficient.  If the old painting shows through, it's just a very faint ghost image, and the stain-blocker layer is still white enough to act as a proper ground.

I don't show it here, but in the plastic container on the left
I have some 90% rubbing alcohol.  This is perfect for
cleaning the brush.

This is a single coat of stain-blocker on the old painting.

5. Finally, once the panel is dry, I flip it over, and if there is writing on the back, I use stain-blocker to cover it up.   Just in case I paint a masterpiece.

I really like painting on these old panels.  The pre-existing texture adds a certain energy to the new painting, and the surface has a nice feeling under the brush.

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