Almost everything in the Museum’s collection gets washed at least once in its lifetime. Having a collection of more than 45,000 objects – that is still growing – means we spend a lot of time washing glass. Every new accession that can be safely washed gets washed. But we also have objects that have been in the collection for a long time that need to be washed.
Why do we wash the glass? The obvious reason is that it looks so much better! We often get asked to wash an object before it gets photographed or put on exhibition.
But that isn’t the only reason, washing the glass actually helps to preserve it. Glass stored in an uncontrolled climate, especially one with high relative humidity (55% and up), is subject to atmospheric deterioration. Although some glass compositions are more susceptible to atmospheric deterioration than others, it can affect glass of any composition if the climate is bad enough for a long enough time.
A more in depth look at atmospheric deterioration will have to wait till another day, but the basic process is as follows: Moisture in the air leaches out the alkali elements from the glass itself. If the alkali is not cleaned off the surface of the glass, it begins to dissolve the silica of the glass, and free up more alkali. If the glass is subjected to cycles of very low humidity, as well as prolonged periods of high humidity, hairline cracks, and eventual crizzling occur. Simply washing the glass and removing the alkali deposits prevents the silica network from being destroyed and keeps the glass in better condition. Grime and pollution can exacerbate the problem.
Unfortunately, we don’t always know the history of the storage conditions that our objects have been exposed to. But we know that even in the Museum the climate has not always been as good as it is now. There are also smoke and nicotine deposits from when smoking was allowed inside the Museum’s galleries (until the mid-1980s) and even some very fine, difficult to remove mud from the 1972 flood.
Which is why, starting around 1998, we began a process to systematically wash every piece in the collection. Most pieces will only need to be washed once because our current climate controls are very good. However, the glass with unstable compositions may need to be washed as often as every couple of years. There are also some glasses which can’t be washed, such as most ancient glass which often has a very fragile surface because of weathering or some modern glasses with water sensitive coatings/paints.
How do we wash the glass?
Glass objects that can be safely washed are washed with tap water and a mild conservation-grade detergent (any mild detergent without dyes or perfumes would work), followed by thorough rinsing with de-ionized or distilled water. It is important to rinse with de-ionized or distilled water because tap water often contains minerals which will deposit on the glass and leave spots. We wash our glass in a plastic sink to help minimize any damage from accidental bumps. Brushes are useful for cleaning cut glasses, soft cotton or paper towels work better for smooth surfaces. We also recommend not wearing gloves because the glass is slippery, especially when it is wet and soapy.
After rinsing, the glass is either toweled dry with paper towels or air dried. For some objects, like bottles with narrow openings, the inside is rinsed with a small amount of acetone to help remove any remaining moisture. Old adhesives from previous repairs or labels are removed with solvents, mostly acetone, ethanol, or a petroleum distillate like naphtha.
Some of you might be thinking it’d be a lot easier to just run everything through the dishwasher, but that is something we never do. Dishwashers are one of the worst environments for glass. Research has shown that dishwashers corrode glass in three distinct processes. The heat and humidity cycling as well as the alkaline environment all play a role. Ever notice haziness or slight iridescence on your glasses at home? Those are sure signs of damage caused by the dishwasher environment.