The Museum’s conservation lab is specially designed for the conservation of glass. While many of the materials, tools, and equipment are commonly found in conservation labs, others are specifically for the examination and treatment of glass objects.
Ultraviolet (UV) lights, both short- and long-wave, can be very helpful in examining glass objects. Many materials used to repair glass fluoresce under UV light, like shellac, which fluoresces orange. Looking at an object under UV light will help locate past repairs and can help identify the material that was used. This helps us decide how to remove old repairs and best move forward with new repairs. In some cases, fluorescence can provide information about the glass itself, but this is not always reliable.
Uranium glasses always fluoresce a bright yellow/green, but some lead glasses fluoresce while others do not. Some other components of the glass composition fluoresce: antimony in Roman cameo glasses often fluoresces a light pink or pink-orange, manganese in Venetian glasses is usually a slight to pronounced yellow, and glasses with a high lead content fluoresce bluish white.
One useful way to examine glass is with polarizing film and a light box. The object is placed in front of a light box with a large sheet of polarizing film taped to it. The light box is turned on and a second sheet of polarizing film is held in front of the object and turned 90 degrees to the right or left. Any areas of major strain will appear as bright spots in the glass. These are almost always related to manufacturing and should be a sign to the conservator that the glass may be very sensitive to rapid changes in temperature, the application of any strain, or sudden shock.
One of the most important (and expensive) pieces of equipment in the lab is the stereo-binocular microscope with a fiber-optic light source, used for detailed examination, documentation (microphotography), and, most importantly, assembly of objects.
A digital balance that can measure weights from 1/100th of a gram to three kilograms is perhaps not the most obviously interesting thing in the lab, but it certainly is a necessity. The conservation team uses a lot of epoxy adhesives, which require precise mixing ratios, and thus need to be weighed accurately.
The lab is also equipped with a low-temperature, or incubator, oven that accurately controls temperature between 35° and 65°C. In general, it is not safe to heat glass, so the higher temperatures (50° – 65°C) are never used. The lower temperatures are primarily used for manipulating the setting time of epoxies in re-assembling and filling losses. Other materials, such as dental wax, Plasticine, and silicone rubber, also benefit from warming. A small refrigerator in the lab is used to slow down the setting time of epoxies.
Almost all of the glass in the Museum’s collection (with the exception of ancient and some modern) gets washed at least once. For that purpose, we have a large plastic sink. The plastic is softer than a metal or stone sink, which helps to prevent damage from minor bumps. The glass is washed with tap water and a mild conservation-grade detergent, followed by thorough rinsing with de-ionized water made at the Museum with a de-ionizing column.
When working with chemicals, safety is incredibly important. Conservators generally use only small amounts of chemicals and try to use the least toxic solvents possible. Treatments that require the use of more toxic chemicals or large quantities of chemicals are done within a fume hood. When not in use, the chemicals are stored underneath the fume hood in a chemical storage cabinet.
Documentation is an important part of conservation, so the lab includes a photographic setup, with a neutral backdrop and good lighting, to take pictures of objects before, after, and during treatment. Photographic documentation is useful in documenting how an object was made or any special features it may have. Often, when an object is broken, the areas that normally can’t be seen become visible and these often have clues to how the object was made and how it might have been used. The photographs taken usually stay in the conservation department, while the Museum’s photography department takes expert images for publication.
Of course, the lab also has plenty of workspace. There are padded tables and counters where staff can examine and treat objects. The tables are movable to accommodate large pieces of glass that come in for treatment. There are also various clamps, stands, and “snakes” (orthopedic stockings filled with polypropylene beads) to support the objects.
For really big pieces and large groups of objects, we have an additional conservation area at our off-site storage facility. This area isn’t fully equipped for conservation, but supports simple treatments like cleaning and minor repairs.