Cleaning the Islamic Bowl

It has been a long time since I last posted, but I have been doing the same project since February. I had a six week break when the conservators went to Egypt, but even so this one project has taken a very long time. I took apart the Islamic bowl and removed all the old gap fills and plaster. Many of the pieces in the central section were laminated. The front and back of these pieces were stable thanks to the glassy glaze, but the porous ceramic in between deteriorated. This resulted in the ceramic crumbling out, leaving two slivers of glaze. At some point, the front and back pieces were sandwiched together with plaster. I took apart all the pieces, including these sandwiched pieces, and removed the plaster. This resulted in 215 pieces of original ceramic, and perhaps as much as a third of the bowl missing.

Three of the five sections. Top right: the top are the original sherds and the bottom are plaster gap fills. Bottom: the plain gray pieces are the backs of painted sherds which have separated.

After removing all the plaster from these pieces, I then had to remove all the adhesive left on the break edges. There seemed to be a couple types of adhesive. The first was water soluble. When I soaked the pieces in warm water to remove the plaster, this adhesive easily dissolved. I just had to brush the break edges to remove it all. However, after drying, a white, solid adhesive appeared on many of the pieces when I checked them under a microscope. It could have been swelled and turned milky due to the water, which is why I did not see it before I started cleaning the pieces.

To remove this harder adhesive, I applied a 1:1 solution of ethanol and acetone to the edges with a cotton swab, which turned the white adhesive slightly 'gummy'. Using a microscope, a scalpel, a pick, and a brush, I was able to scrape off the adhesive. It was hard work as it did not want to come off. This stage of the process took up most of the time I have spent working on this bowl. This week, I finally finished.

Next, I need to consolidate the pieces. This involves painting on a 10% solution of Paraloid B-72. The weak adhesive will protect the pieces, sealing them and stopping them from crumbling further. I made up the solution this week to use next week.

Paraloid B-72 comes in solid, clear pellets. I measured out 20 grams of Paraloid and just under 200 ml of acetone. Technically, a 10% solution needs a 1:9 ratio, but Claudia said she tended to measure out a 1:10 ratio because the solvent evaporates and on excavations it is easier to round up. I then wrapped the pellets of Paraloid B-72 in gauze and tied it with thread, creating a bag. This was placed in the jar of acetone so that the bottom touched but the majority was out. By suspending the bag, I did not have to keep shaking or stirring the jar so that the adhesive would not just settle on the bottom. The jar is then left for 24 hours to allow the adhesive to fully dissolve. Next week, it will be ready to use.

 Top left: Measuring out the Paraloid B-72. Top right: Suspending it in acetone. Bottom: Paraloid dissolving in the acetone.