The Osler Candelabrum and incipient crizzling

Posted on December 6, 2012 by Astrid van Giffen

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 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

Exhibition on Louis C. Tiffany features Stained Glass Window from Corning Museum

Posted on October 23, 2012 by Yvette Sterbenk

Louis C. Tiffany and the Art of Devotion, an exhibit currently on view at the Museum of Biblical Art (MOBIA), in New York City, showcases the array of church decorations and memorials that Louis C. Tiffany (1848-1933) produced beginning in the early 1880s. On view through January 20, 2013, the exhibit shows the breadth and depth of the firm’s oeuvre, and the place Tiffany Studios created for itself in American religious art.

The centerpiece of the exhibition is a Corning Museum artwork, The Righteous Shall Receive a Crown of Glory (96.4.230). The window, which measures 12’ 10” x W. 8’1, was created for the United Methodist Church of Waterville, New York, around 1901.

Warren Bunn, CMOG’s manager of exhibitions and collections examines the window pre-conservation with Drew Anderson, conservator at the Metropolitan Museum of Art and independent curator Diane Wright.

When the window was removed from the church, it went into the collection of Mr. and Mrs. Bruce Randall. The couple offered it to the Corning Museum in 1996. At that time, it was too large for the Museum to display in any of its gallery areas and needed restoration work. However, since one of the most important roles of a Museum is to collect and preserve important objects for the future, the donation was accepted and the window stabilized for storage.

Curators and conservators from The Corning Museum of Glass and the Metropolitan Museum of Art examine the window to assess conservation treatment.

When MOBIA began planning its Tiffany exhibition, it approached the Corning Museum about this window. Several institutions then came together to complete conservation work on this beautiful object. CMoG offered its existing conservation report to facilitate work on the window. The Neustadt Collection of Tiffany Glass offered conservation studio space where the treatment could take place. MOBIA incorporated the cost of the restoration into its exhibition budget.

The window was secured in 12 custom-built crates at CMOG and taken to the Neustadt Collection of Tiffany Glass in July 2012. Over the summer, it was restored by Drew Anderson, a conservator at the Metropolitan Museum of Art who specializes in stained glass.

Preparing to install at MOBIA.

When the exhibit at MOBIA ends, the window will come back to Corning, and the curatorial staff are working on trying to find a space to display it. We’ll keep you posted.

In place at MOBIA. The window measures 12’ 10” x W. 8’1.

The bead that fell apart

Posted on August 9, 2012 by Astrid van Giffen

As you can imagine, glass deterioration greatly affects the strength of a piece of glass, but why would a weathered glass spontaneously fall apart after years of apparent stability? We recently had that happen.

64.1.13 before it fell apart

The piece in question is a core-formed bead dating to 500-250 B.C. The bead is made of opaque white glass with trails and prunts of blue, yellow, turquoise, and red-brown glass, and was heavily weathered with a bubbly and pitted thick milky-white weathering crust with patches of dark enamel-like weathering over the entire bead. It has been in the collection since 1964 and had appeared stable. The bead was recently photographed and, to our surprise, an hour or so after it was photographed and safely replaced into a plastic bag, the bead was found broken into 3 larger fragments and numerous small bits.

64.1.13 broken into 3 larger fragments and numerous small bits

So what happened? Direct physical causes may have contributed but do not seem to be the main reason that the bead fell apart, which points towards the glass deterioration itself and environmental factors, especially temperature and relative humidity (RH), playing a role. Blackish dendritic staining (possibly manganese) on all the break edges indicates that there were cracks in the glass which had already gone most of the way through the width of the bead. It is likely that these structural weaknesses along with (slight?) climate changes and the stress from transport and handling caused the bead to break.

Detail showing blackish dendritic staining on break edge

Was this preventable? Maybe not, but to better understand what happened we need to determine if the bead could have experienced any changes in temperature and RH and how big those changes would need to be to affect the glass. In this case the main source of possible climate changes is the photography studio itself, specifically the lighting. We’re hoping that a repeat of the conditions, monitored with a data logger, will give us some insight into the effects lighting for photography has on the ambient temperature and humidity, especially on days when the lights are used for a long time.

Solving an ancient puzzle in the Conservation Lab

Posted on July 19, 2012 by Astrid van Giffen

This summer the Conservation Lab is filled with fragments, even more than there usually are. All these fragments of Islamic lustre and stained glass don’t belong to one object. Most of them were once part of the extensive fragment collection of Ray Smith and came into the Museum’s collection in two batches in 1951 and 1968.

Islamic lustre and stained glass fragments in the conservation lab

Although fragments aren’t as visually pleasing as whole or nearly whole objects, they still provide a lot of information about glassmaking techniques. It is also a lot easier to take a sample for analysis from a fragment than from a complete object.

Individual fragments in baggies waiting to be sorted

In order to really study fragments like these, we need to be able to keep track of them just like any other object. Unfortunately, the Museum’s record keeping wasn’t always as comprehensive as it is now and many of these fragments were never formally accessioned. As you can imagine, accessioning and cataloguing hundreds of fragments is a big job. We’re trying to reduce that number by looking for joining fragments. This might sound like looking for a needle in a haystack, and in some ways it is, but laying out all the fragments in one place and arranging them according to colors and patterns makes it a little easier.

More fragments

We have found several joins already!

fragments waiting to be joined

After we get done with all the lustre and stained fragments, we get to start the whole process again with our enameled Islamic fragments.

Enameled Islamic fragments waiting for the next round of join finding

Re-fusing a Bomb

Posted on May 25, 2012 by Astrid van Giffen

The installation of exhibitions always requires a lot of glass to be moved in a short amount of time. Although our preparators are excellent at moving glass without damage, sometimes gravity happens. During the installation of our Making Ideas exhibition that opened May 19, the fuse was broken off of one of the glass bomb prototypes designed by Steven and William Ladd. Luckily it was just one break and the piece was treated in time for the opening.

Glass bomb with the broken fuse before treatment.

Glass bomb prototype with the broken fuse before treatment.

Glass bomb prototype during treatment. The bomb had to be positioned in such a way that the fuse would stay where it needed to be because the adhesive we use takes a long time to set.

If you visit the Museum, look for the bomb in the Making Ideas: Experiments in Design at GlassLab exhibition, now on view through January 6, 2013.

Taking down The Glass Wall, Part 2

Posted on January 20, 2012 by Astrid van Giffen

With team work and good planning the de-installation of Brian Clarke’s The Glass Wall went off without a hitch!

Removing the glass panes one by one

In three days our team of three preparators, one collections and exhibitions manager, two conservators, and two outside contractors removed all 245 panes of glass, and all of the hanging hardware and steel support structures. Most of the work was carried out by our outstanding preparators who had to climb on ladders and scaffolding to reach and release all of the glass components.

Each large section of the window is made up of 35 smaller sections held in place with hardware and various set-screws. To dismantle, one person supports the adjacent glass panes, and the other loosens the set-screws. Once released, each panel is then handed down to another person and placed into specially constructed slotted crates. What makes it particularly difficult, is all of this is done some 30+ feet above the floor level!

Stephen hands off a glass pane

Most of the panes were in excellent condition, although they were extremely dirty. There were about a dozen panes with loose cames which will need to be reattached. One pane had an old break in it. It had been repaired previously, but needed a little clean up in the lab.

The glass panes are packed for safe transportation

One thing we hadn’t thought about in our extensive planning was that the panes would be slightly loose in the slotted crates. We realized it quickly and improvised with small squares of volara (closed-cell polyethylene foam) and acid-free board tucked around the panes to prevent them from rattling while they were moved. We also found that some of the panes were slightly wider than others. Luckily the difference was not a big enough to be a problem.

Now that the panes are safely in our offsite storage facility, the next step is to clean them and repair the loose caming.

See more photos of taking down The Glass Wall: http://flic.kr/s/aHsjy8cdZ4

by Warren Bunn, Collections and Exhibitions Manager and Astrid van Giffen, Assistant Conservator

Taking down The Glass Wall

Posted on January 9, 2012 by Astrid van Giffen

Brian Clarke's The Glass Wall

A new year brings new challenges. One of our challenges this year is to deinstall the very large Brian Clarke window, The Glass Wall. It is currently located just inside the Museum’s western façade along the ramp to the upper entrance of the magic of glass theatre. It is made up of seven large panels each with 35 individual panes with metal supports suspended from steel cables with specially made hardware. The window is 6.3 m (20 ½ ft) tall and 22.4 m (73 ½ ft) long and hangs at the second story level. This is going to be a BIG project!

Brian Clarke's The Glass Wall with the GlassMarket Cafe below.

This spring we are renovating the GlassMarket Café, which sits in the space directly below the window. While the renovations occur (the Café reopens in April) the location is unsafe for the window. Deinstalling the window will also allow us to clean it and repair the loose cames (the aluminum strips around each glass pane) found on some of the panes. The size and location of the window make any kind of treatment in situ almost impossible. The window badly needs to be cleaned since neither it nor the interior of the building’s windows have been cleaned since it was installed in 2000.

A loose came on the bottom of a pane.

As you can imagine, deinstalling such a huge object is not a process that is undertaken lightly. Dismantling the window requires a lot of planning and preparation. Over the last few months we’ve been having meetings with everyone involved to do just that. This includes the Museum’s conservators, preparators, registrars, and operations managers, as well as an outside contractor who will provide scaffolding and remove the hardware for hanging the window.

The Glass Wall. At the top of the ramp there is about a 2 foot gap between the window and the ramp.

We also had to think about how to store the 245 panes of glass while the window is off display. We had special crates made with slots for the panes which will make transporting and housing the glass safe and compact. The window will be dismantled and taken to our warehouse where we will set up a special area to clean the glass and do any necessary repairs.

Specially made crates with slots to hold individual panes.

The Glass Wall. At the bottom of the ramp there is only a very small gap between the window and the ramp.

After the scaffolding has been put up, the window will be carefully removed, pane by pane, by our preparators. Any loose cames they come across will be temporarily secured with tape. Once all the glass has been safely packed and taken away, the support system can be taken down by our operations team and the outside contractors.

The whole process starts this week!

Washing Glass

Posted on December 9, 2011 by Astrid van Giffen

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.

Filling losses with Paraloid B-72

Posted on November 1, 2011 by Astrid van Giffen

Last week chief conservator, Stephen Koob, and I were in Ottawa at the Canadian Conservation Institute’s “Adhesives and Consolidants for Conservation: Research and Applications” Symposium.

We went to present a new technique for filling losses in glass which was developed at the Corning Museum of Glass. For this blog I thought I’d tell you about one of the objects I recently used this technique on. This Islamic beaker is interesting for other reasons as well. During the initial examination I noticed glue on break edges for which I didn’t have any joining fragments. This lead to the discovery of a box of loose fragments in our storage area labeled with the same accession number as the beaker. Some of the fragments in the box definitely belonged to the beaker, but others clearly did not. Although no previous treatment records were found, the object had certainly been treated in the museum in the past. These extra fragments were probably used as fill material for the losses in an even earlier treatment that occurred before the beaker came into the museum’s collection.

74.1.18 Before treatment

The object in question is an Islamic beaker dating to 900-1199 A.D. It came into the lab because the old repair partially failed during handling. The beaker was broken into 5 sections of multiple fragments and 2 individual fragments and had about 15-20% of the body missing. Much of the severely weathered surface of this beaker has already been lost, leaving the remaining glass very pitted and much thinner than it originally was. Surface loss and pitting also occurred along the break edges causing the fragments to not join well. Missing pieces caused some fragments to be almost “floating” because they barely touched any adjoining fragments. Too much pressure was put on these fragile joins during routine handling, causing them to fail.

The fragments and break edges were cleaned and re-assembled using Paraloid B-72 adhesive, including many of the fragments found later. Next the larger losses were filled. This was done by casting films of B-72 in silicone molds. The film was then “textured” by allowing lots of tiny bubbles to form by placing the film in the oven on a smooth surface. The result was very complementary to the weathered surface of the beaker. The B-72 film was placed over the loss in the object, and the shape of the loss was traced onto the film and cut out with scissors. Finally the fills were put in place and glued onto the glass with a small amount of acetone on a soft brush.

74.1.18 After treatment

The paper we presented at the conference has more details about the technique of casting B-72 for fills in glass. It will be published online at the CCI website later this year.

Glass Corrosion: Weathering

Posted on September 14, 2011 by Astrid van Giffen

Group of archaeological bottles with varied weathering.

We tend to think of glass as a very stable material that doesn’t corrode, but that isn’t always true. Glass can and does corrode. The chemical that is most harmful to glass is something we consider fairly harmless, namely water. Water leaches out the alkali components (sodium and potassium) from the glass causing microscopic damage. This process generally takes time, so washing your glasses in water is safe. The composition of the glass is also a contributing factor. Some glasses have a much more stable composition than others.

Piece of archaeological window glass with severe weathering seen under a microscope. The red arrows point to areas where the glass surface has collapsed into itself.

The iridescence and discoloration seen on many archaeological glasses is a form of glass corrosion known as weathering.

During burial, moisture in the ground leaches out the alkali components from the glass, leaving behind distinct silica-rich layers alternating with layers of air. These layers are usually extremely thin, but numerous. They interfere with the direct transmission of light through the glass which causes the iridescence. The layers may be uniform and compact, or flaky, fragile, and discontinuous.

The discoloration of the glass is caused by the migration or alteration of coloring ions or other trace elements. The ions can be leached out of the glass or be taken up from the environment. For example, iron and manganese turn black, while contact with copper corrosion can cause green staining. Certain ions, most notably manganese and copper, may change color through oxidation.

Detail of weathered glass surface.

The burial conditions and the composition of the glass both contribute to the extent and appearance of the weathering which can vary extensively even within a single piece of glass. Glass buried in dry environments will have little to no corrosion, while glass in moist burial environment will generally weather extensively. The acidity of the burial also influences the extent of corrosion. Glass is fairly resistant to acids and even highly acid (low pH) environments will do little damage to the glass unless fluoride or phosphate ions are present. Alkali (high pH) environments are much more damaging to glass because the silica network is attacked and broken down.

55.1.84 This first- or second-century glass statuette of Venus has very thick weathering layers which have been lost in some areas.

The thickness of the weathering can vary greatly depending on the chemical stability of the glass and the aggressiveness of the burial conditions. In extreme cases corrosion products may have completely replaced the original glass. Underneath the weathering the so-called glass core retains the original composition and color of the glass.

One may be tempted to remove the weathering to reveal the original color, and that was certainly done in the past. However, unlike corrosion on metals, glass corrodes from the outside inward and the weathering preserves the original surface. Any details of the surface such as tool or usage marks or even fine decoration will be lost if the weathering is removed. The glass underneath the weathering is usually unevenly preserved and may be pitted or appear etched. The original smooth surface of the statuette of Venus in the image to the left is perserved in the intact weathering, but the core glass exposed where the weathering has been lost is severely pitted.

Weathering is a type of corrosion found on archaeological glass, but historical, modern, and contemporary glasses are affected by another type of deterioration known as atmospheric corrosion, crizzling, weeping, or glass disease. I’ll save my discussion on that for another time.

Corning Museum of Glass

Behind the Glass

Category Archives: Conservation