The key to successful preservation is retreatability. Many of
the finishes that were customary before the second quarter of the 20th
century are still easily soluble in alcohol generations later. Although there
is an obvious real life potential for a careless spill of alcohol, the long
term benefits of resoluble (i.e. thermoplastic) coatings are inestimable. If you are looking for your work to last 200
years use shellac for varnish and hide glue for adhesive. Period.
When these old “spirit varnishes” are crazed and
deteriorated after 150 years it is possible through the introduction of alcohol
to redissolve and rework the coating. This treatment has the benefit of
readhesion to the substrate, amalgamation of the coating (restoring cohesion),
and restoring the “optical saturation” of the finish (For when a finish is
described as “dry and lifeless”).
There can be other problems with finishes, however. In some
cases, varnishes exposed to the sun’s UV rays for an extended period can lose
their color. Occasionally, solvent action alone can remedy this but in extreme
cases more is needed.
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Before Treatment |
This chest of drawers I worked on recently was severely sun bleached
and application of solvent alone wasn't retrieving the original color. Because this
finish was soluble in alcohol I was able to restore the color without stripping
away the coating.
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Before Treatment |
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Before Treatment - Notice original color preserved under the brasses |
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The Materials |
This was my method: TransTint metallized dyes well diluted in
alcohol padded into the damaged coating. I prefer this method over spraying a
toner because I find hand application much more discriminating with regard to where
it lands. (Overspray into secondary areas is common.) As long as the dye is
well diluted, I can safely work my pad with a wet edge on one surface at a
time. It’s important to avoid stopping mid-pass as this can leave a tell-tale
mark. To be honest, this technique does require experience and practice. It
takes a controlled touch to keep everything even but I like how fine-tuned the
application can be.
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Quick passes are required |
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During Treatment |
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During Treatment |
After all the dye was applied over each surface (20-30 quick
applications), it was left to dry. In order to lock the color in, I later padded
10% Paraloid B-72 in toluene lightly over the piece. After that was dry I was
able to pad a couple coats of shellac.
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During Treatment |
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Color complete |
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Paraloid B-72 in Toluene |
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Sealed |
A final rubbing and paste wax completed
the treatment. Though the dye is not entirely retractable, the original
finish was retained and the color was restored.
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After Treatment |
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After Treatment |
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After Treatment |