The Croll Testimonial: Acetone, patience and paperwork

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Six putti from the lower basin

This might sound like a morning's work but giving individual attention to a total of one hundred and ten pieces (not counting nuts) is a slow and methodical process. All the components now have numbered tags to make sure everything goes back together the same way it came apart, and the tags are made from thick copper foil rather than paper so they won't disintegrate in water or solvents.

I've carried out some solvent tests to find out the best way of stripping the lacquer, and the results were really not what I was hoping for: Acetone? No effect. Dichloromethane? No effect. Every other solvent in the workshop? No effect. It looks as if the surface has been coated with a heat cured lacquer of a type popular for use on silver in the 1960s and 70s, and the only way I have found of removing it is by immersion in a hot solution of sodium hydroxide (caustic soda) for about an hour. The health and safety implications of this are considerable, not to mention the logistics of making a heated stripping bath big enough for the half metre wide base of the Croll, so there is still quite a lot of careful planning and paperwork to go before I can begin work in earnest.

Two of the silver garlands before (top) and after de-lacquering

If the de-lacquering is going to be done using sodium hydroxide all fifty nine of the bezel set cabochon stones in the Croll will have to be removed to protect them from damage. Luckily the stones are set in a way I've never seen before, with the stone set in a deep bezel which is in turn pushed into a socket soldered to the object. As the settings are only friction fitted into the sockets most of them could be eased out using that most indispensable of conservation tools, the thumb.

A few of the settings have been adhered into their sockets using what looks like Araldite or a similar two-part epoxy and these are proving much more challenging to remove. Heating or immersion in solvents are both undesirable options while the stones are still in place, so I have tried injecting acetone into the settings with the hair-thin needle of an insulin syringe. Because of the rapid evaporation of the solvent I needed to introduce more every few minutes but the adhesive did eventually soften enough for me to remove some of the settings.

Injecting acetone into the settings

The last four are still refusing to budge so I may need to come up with an alternative method of releasing them.

Since things are starting to come together (or apart), this seemed like a good time to write a blog update. It's good to be making a real start on this project, and having seen the difference made by removing the lacquer I'm looking forward to starting full-scale treatment.