Reversibility...Priceless!

Windsor Bench on the Bench

I have used different kinds of animal protein glues for over 40 years in all types of applications.  I began using these glues since I was concerned about proper conservation and restoration of period antiques, and that was the only kind of glue available to those pre industrial wood workers.

I thought, "If it worked for them, why change?"

One of the most important rules in restoration and conservation of early objects is that the repairs must be "reversible."  That is because it may happen that subsequent research into certain objects may suggest that the current repair was not done properly and needs to be removed so that more appropriate work can be done.

This applies to glues and finishes.  I remember very clearly the summer of 1978, while I was attending the Summer Institute at Winterthur.  They have in their collection a magnificent high chest made in Boston around 1740 by John Pimm.  It is without a doubt the finest example extant of its type, and is distinguished by the superb preservation of its decorative surface.

I had visited Winterthur many times before and always took some time to stand in front of this piece and examine its surface carefully.  You could see the marks of all the owners in the small scratches and marks of use which were clearly visible, and yet the surface was as beautiful as the day it was made.

That summer, when I went into the collection to visit this piece, I was shocked.  It was covered with a high gloss surface, which reflected the light and made it impossible to see the character of the surface.  It looked, frankly, like a piece of formica.  I asked around and was told that it was a new DuPont finish that was being used for "conservation" of the surface.  I was assured that this new finish, should it be determined to be inappropriate, could be removed by a "special solvent" that was designed for this purpose.

There is no reason I can think of to "experiment" with this new finish on one of the most important objects in the collection, and this example of improper conservation represents a dark period in what is otherwise a very conservative museum policy.  I note that this finish has now been removed and the Pimm highboy is supposed to be back in its "original" condition.

When it comes to glues, reversibility is just as important.  All furniture experiences damage at some point in its life, and it is essential that the glues can be reversed to allow for the structure to be taken apart and repaired.  From time to time a client will bring in a modern copy of an oak chair, which was made in some other country with epoxy holding the spindles in place.  I have to tell them that there is no way to repair it, except to start over.  You just loose money with cheap furniture.

All protein glues, on the other hand, are completely reversible, by using heat and moisture.  You can take an Egyptian chair and reverse the glue.  It doesn't matter how old the protein glue is, it will always reverse with the proper amount of heat and water.

Like water, which can change from solid (ice) to liquid (water) to gas (steam) simply by changing the temperature, animal protein glues can easily change from solid to gel to liquid and back again as a function of heat and moisture.  All you need to do is understand whether to add heat alone or water alone or heat and water together, depending on the condition of the glue, and you can make it do whatever you want.

Most people are concerned about "reversibility" of the glue meaning that it will "fall apart" given the right conditions.  In fact, normal furniture construction has a finish, which protects the wood, which, in turn, protects the glue from exposure to moisture.  Heat alone will not do it.  Properly cured glue can stand extreme temperatures, when there is no moisture present.  On the other hand, long exposure to cold water will soften even the oldest glue and turn it to gel.  By long exposure, I mean soaking in water for several days.  Normal furniture doesn't have to worry about that, except for floods.

A case in point happened this week when a chairmaker in Australia contacted me about a glue up problem.  He has been using Old Brown Glue, which he finds perfect for Windsor chairs since it is easy to clean up and has a fairly long open time.

Go Soak Your Head

This time of year it is winter in Australia, and the shop was not heated.  He warmed up the glue and started to put his bench together, but when he went to put on the crest, the glue was cold.  As he tried to seat the crest on the 17 spindles it stopped short.  On one end it was 6mm from seating and the other end 11mm from seating.  Nothing he could do would move it.  He tried hitting with a mallet but it wouldn't budge, and he couldn't get it off.  That glue grips when it sets.

He reached for the heat gun, but that only dries out the glue. Nothing worked, so he contacted me.
I told him that he needed to first hydrate the glue.  The only way was to soak the crest, allowing the water to penetrate the wood fibres and thus reach the glue surface inside the joint.  Once that was done, he could simply heat the joint and it would open.  

He wrote back a few days later with a report of success.  He had soaked the crest and then heated it up, and, in his words, "The crest rail slipped off without a blow."  Problem solved.

200 years from now, if someone wants to remove that crest rail, it will still be possible, since it was put on with animal protein glue.  "Reversibility" is what keeps antiques alive for future generations.

Ready To Glue Up Second Time