Saturday, November 29, 2014

Resurrecting a Sun Bleached Finish


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.

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.

Before Treatment

Before Treatment - Notice original color preserved under the brasses

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.

 Quick passes are required

During Treatment

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. 

During Treatment

Color complete

Paraloid B-72 in Toluene

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. 

After Treatment

After Treatment

After Treatment

6 comments:

  1. very well done, how many hours went into this project. also after the finish was complete did the metal get ant type of treatment.

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    Replies
    1. Thanks. The treatment time was somewhere around five hours with lots of dry time between stages. The brasses were left untouched.

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  2. I don't understand why a coating of B72 was applied atop your tinted finish if you wanted then to apply a coating of shellac on top of that.
    "Though (not)* the dye is not entirely retractable, the original finish was retained and the color was restored."
    I don't quite follow the compelling need in this case for maintaining the last vestiges of an original surface finish when the wood surface itself has become so degraded if that is how I understand your motivation for having chosen this procedure.
    Would you also relate what kind of conditions led to such a sun bleaching?

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    Replies
    1. The B-72 has a different solubility than shellac so it was safe to pad a sealing coat on. If I had gone directly to padding shellac some of the color could potentially come up. Also the B-72 is reversible in toluene in case anyone ever wanted to separate my shellac applications from the original.
      The wood surface was not degraded. The coating itself was degraded but was still able to be manipulated as described here. Every time a piece is stripped to raw wood, you lose part of its history. If I can save it, I will.
      This thing must have been parked right in front of a southern facing window for many years.

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  3. A great looking result on the finish.

    The chest of drawers itself look a bit peculiar.
    Kind of like someone started out wanting to make a Shaker like piece. The sides and the top and the fall front look very "simple", without any fuss and just a small beading on the sides.
    Maybe their wife suddenly decided that she would like to have a curved front, and this was done. Then they added some ball and claw feet to match the front.
    I think it is especially visible on the 3rd last picture (complete view after finish).
    What is you opinion, do you think that style was changed sometime during the construction?
    Brgds
    Jonas

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    Replies
    1. No. It is a factory reproduction piece. The proportions on these guys are often bizarre. Thanks, Jonas.

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