by Meghan Smith, Conservation Specialist
In the Indiana State Museum conservation lab, we employ a lot of cleaning methods that would probably surprise you. Historic clothing, for example, almost never gets washed in the traditional sense; instead, we use vacuum cleaners to remove dust and dirt from the fabric. Paper artifacts get cleaned with something fairly normal – an eraser – but the eraser is ground into bits first, which are then gently massaged on the surface.
It’s been a long time since she had a bath.
But sometimes, even we think our methods are unusual. A recent example of this was a marble statue, which was brought into the lab for a checkup before going down to the historic Culbertson Mansion State Historic Site in New Albany. It’s a small-scale copy of a statue called Venus Italica, sculpted by the Italian artist Antonio Canova around 1812. Numerous copies can be found in museums and private collections throughout the world, while the original is in the collection of the Pitti Palace in Florence, Italy. According to our records, this particular copy was purchased by Mrs. Francis Heberly during a trip to Florence in 1887. After living through more than a hundred years of coal dust and grit, the Venus was looking pretty gray. We cleaned off larger patches of grime using an adhesive putty called groomstick, and then attempted spot cleaning using cotton swabs and a very mild detergent solution. Unfortunately, this cleaning method created an uneven, patchy effect on the statue’s surface.
This is where the unusual method comes in. In order to achieve an even appearance on the surface, we decided to mix up a poultice. If you’ve heard of poultices before, it’s probably in the context of pioneer medical remedies, where a poultice meant a kind of mash made up of medicinal plants that would be plastered to a wound. In this case, it means a thick, gelatinous mixture spread over the surface of a marble or granite statue to remove stains.
Mixing up the poultice was a little bit like taking chemistry all over again, although (with apologies to my excellent high school chemistry teacher) the practical applications were easier to grasp. Most of the poultice is water, which is the actual solvent that does the cleaning. But to get it to stay in place, it has to be a lot thicker than plain water. Accordingly, the water is mixed with methyl cellulose, which is a thickener that can be found in some shampoos, paint and even ice cream. Movie fans will be
interested to note that methyl cellulose mixtures have been used in many films, including Ghostbusters (ectoplasm!) and Aliens (acidic alien drool!). But these two ingredients don’t get the job done on their own. Ammonium hydroxide is added to keep the poultice’s pH basic, so as not to etch the surface of the marble. Finally, fumed silica powder and propylene glycol are added to make the poultice even more viscous and elastic.
Once applied, the poultice made the Venus look like a melting candle. We had to babysit the drying process, pushing the gel back into place when it threatened to ooze off her limbs.
After about two days, the last of the poultice had hardened into a thin, crackly skin. We peeled it back, and voila! The dirt came with it.
Peeling off the poultice was extremely satisfying.
Because the layer of grime was so thick in places, we ended up doing multiple applications of the poultice. The most stubborn area proved to be the backs of her legs, due to the gravity-defying angle of the surface. In order to get the poultice to stay put long enough for the water to do its work, we wrapped the gelled area with cling film and left it for a few days before allowing it to dry.
Post-cleaning. What a difference, huh?
After some additional mechanical cleaning to even out the last few patchy areas, the Venus was ready for her debut!
To see the Venus and other beautiful 19th century decorative and household items, visit the Culbertson Mansion State Historic Site in New Albany! It is a truly stunning example of Victorian glamour.
The Venus Italica in her new home at the Culbertson Mansion.
Filed under: Culbertson Mansion, history, museums, science, State Historic Sites | Tagged: ammonium hydroxide, Antonio Canova, chemistry, conservation, methyl cellulose, Pitti Palace, poultice, propylene glycol, silica powder, Venus Italica | Leave a comment »