- These 100-year-old cloisters are cleaned using gel poultice to remove any dirt, grime, and oils.
- The gel poultice traps the dirt and grime, and then it’s peeled off in sections.
- An ultraviolet light reveals any remaining gel.
Emily Cummins: I’m Emily Cummins. I am the assistant objects conservator at the Toledo Museum of Art in Toledo, Ohio. I’ll be walking you through how we use a gel poultice to deep clean the columns, capitals, and archways in our medieval cloister gallery, which dates’ range from the 12th century to the 15th century. So, this is the first time that these arcades have been deep cleaned since their accession at the Toledo Museum of Art. Almost 100 years’ worth of dirt and grime is accumulated on the surface. The cloister gallery at the TMA is composed of multiple pieces of various cloisters. They’re all from southern France. Although the elements of the cloister have been dry cleaned over time, they really hold on to the dirt and oily grime in the surface in those network of pores in the upper layers.
So, we decided to start on the columns because they are generally smoother than the capitals, for instance, which have carvings that are more three-dimensional, that stick out more into space, and are therefore a little bit more difficult to apply an even layer of gel to.
First, the gelling agent is mixed with water without any other cleaning ingredients added. This is done so that the gelling agent can really hydrate as much as it needs to, so we don’t have clumps in the final gel. Now, once the water and the gelling agent sit together for 10 to 12 hours, then we’ll add the rest of our cleaning ingredients. Now, in the gel we have two cleaning ingredients. One’s surfactant, and one’s soap. The surfactant helps break the interfacial tension between the grime and the stone, and the soap helps dissolve all of the oils that are in the grime. We also use a plasticizer, which allows the dried film to be a little bit more flexible and easier to peel off. And then, finally, we have a small amount of a drying agent, which helps set the film on the surface of the stone to minimize the amount of dripping that we have, because we are fighting against gravity. Stone I think generally appears to be a really robust material, but it’s actually really porous, marble and limestone in particular. The gel, when it’s applied to the surface, sort of uses capillary action. The water in the gel impregnated with those cleaning ingredients is forced into the pores of the stone and helps break the bond between the grime and the stone. And it’s sort of a cyclical process. So as more water gets pushed into the stone, that grimy water gets pushed out, and all of the dirt and grime gets trapped in that gel film. So, we apply the gel with a brush to the stone in a relatively thick layer. As the water evaporates from the gel, the layer shrinks. So the gel is over 90% water. And so we are getting some dimensional shrinkage, and so the wet application needs to be a little less than a quarter of an inch thick, which is rather thick. But a thicker wet application will lead to an easier dry removal. So, the gel is checked periodically as it dries to make sure that it’s drying evenly. If we need to move the fans, we go ahead and do that. To make sure that the gel is sufficiently dry for us to peel, we really just check it with our hands, sort of testing the temperature and seeing if it’s a dry, hard film or a wet, jelly film.
So, once the gel film is fully dry, we can start the mechanical removal process to take away all of that dirt and grime that’s collected in the gel. But generally speaking, we’ll use bamboo skewers to actually sort of poke a little hole into the gel underneath it so that we and our participants can really start the peeling process. And it’s really important that when we peel the gel, we use what’s called a sheer pull. So taking a loose flap of gel and folding it back 90 degrees and peeling it off that way, so that it’s less abrasive to the stone. Once the gel is dry, what we’re seeing is all of that dirt and grime which has accumulated in the stone over time trapped onto the surface and really trapped within that gel. So when we remove the gel, we are removing almost 100 years of dirt and grime with it.
So, after the broad sections of the dried gel film are removed, we check all of the surfaces with ultraviolet light. We use handheld UV flashlights to check the surfaces to see if there’s any residual gel film. The gel fluoresces under UV light so that we can really easily spot any leftover residue and really go in strategically and remove those sections. So, once all of the surfaces are checked with ultraviolet light and all of that gel film is removed, the final step to really make sure that the surfaces are cleared from all of that cleaning solution is to use wet cloths to actually wipe down all surfaces. This will also rehydrate any remaining gel on the surface so that it becomes really noticeable to the naked eye, so that anything that we missed with the UV lights can then be removed. It’s been very rewarding to see the volunteers come together to have a sense of community and ownership over this really beloved space at the Toledo Museum of Art.