Tag Archives: washing glass

The Osler Candelabrum and incipient crizzling

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We recently had parts of a huge candelabrum in the lab. The piece was made by the English glass company, F. & C. Osler, around 1883, and stands almost 10 feet tall. Luckily the whole object did not need to come to the lab; only the tulip shaped shades were brought so that they could be washed.

The Osler candelabrum (96.2.10)

The Osler Candelabrum (96.2.10)

The candelabrum's shades waiting to be washed.

Some of the shades are replacements for missing original ones. These replacement shades are made from a different glass than the originals, one that has an unstable composition. They are in the first or incipient stage of a degradation process known as “crizzling,” sometimes referred to as glass disease.

Two of the candelabrum's shade. The original on the left is clear, while the replacement on the right has become hazy because of incipient crizzling.

Crizzling is affected by two main factors, the composition of the glass and the climate in which it is kept, especially the relative humidity. During the crizzling process, moisture in the air leaches out the alkali elements of the glass which accumulate on the surface. The alkalis on the surface attract more moisture, sometimes to the point of forming droplets on the surface. This symptom of incipient crizzling is known as “weeping.” If the climate is drier, the alkalis can form as crystals. The alkalis also turn the surface hazy and slimy and have a distinct smell which I like to describe as dusty vinegar. A buildup of alkalis on the surface not only looks bad, it is also bad for the glass because it creates an alkali solution that starts breaking down the silica network of the glass. If the crizzling continues, the structure of the glass is eventually so compromised that the glass falls apart. The composition of the glass plays a huge role in how long it takes to reach the final stage of crizzling. Usually it takes many centuries, but if the composition is really unstable the glass can disintegrate in just a few years.

One of the shades being washed. The conservation lab has a plastic sink for washing glass to help prevent damage from accidental bumps.

Unfortunately, there is no way to reverse the crizzling process; the best we can do is slow it down. We do this by washing the glass to remove the alkali buildup and by making sure crizzling objects are kept in a stable environment. Air circulation around the objects also helps evaporate moisture on the glass surface.

The replacement shades on the Osler Candelabrum turn hazy about every 5 years which is when we bring them into the lab and wash the alkalis off the surface. The washing is done with tap water and a mild, conservation grade detergent, followed by thorough rinsing in de-ionized water to remove the minerals left by the tap water. The original shades were a little dirty, so we washed those as well.

The clean shades back on the candelabrum in the galleries.

More on crizzling: http://www.cmog.org/article/crizzling
View the Osler Candelabrum in the collections browser: http://www.cmog.org/artwork/candelabrum-0

Washing Glass

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Glass waiting to be washed

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.

Two glasses before and after washing

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.

Two bottles with mud from the 1972 flood on them.

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-1980’s) 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.

A cart of glass before and after washing.

How do we wash the glass?

Washing 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 removeany remaining moisture. Old adhesives from previous repairs or labels are removed with solvents, mostly acetone, ethanol, or a petroleum distillate like naphtha.

This modern juice glass was once clear, but years of being washed in a dishwasher has given it a cloudy and etched appearance.

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.