This week’s blog post comes to us from the Museum’s 2023 conservation intern, Theresa ‘Terri’ Costello. Terri is originally from New Hampshire but has spent the last eight years studying in Europe. Terri has a Bachelor’s degree in ancient history and archaeology from Trinity College Dublin, a Masters in conservation and restoration of glass and ceramic cultural heritage objects from the University of Amsterdam, and is currently finishing up a two-year post-Masters in Amsterdam. During her internship at Corning, Terri carried out practical treatments of objects and conducted research into the composition of Carder’s Mandarin Yellow glass. You can follow Terri’s conservation journey on Instragram: t.costello.conservation
Having an object come apart in my hands was not something I expected to happen during my internship, but there are always surprises when working closely with museum objects. As the conservation intern for the summer, one of my tasks was to conduct condition checks on objects being moved to different locations within the Museum or going on loan. One such object was a Steuben Glass vase, which was being relocated from the Carder Gallery to make way for the StudioNEXT project. Handling fragile objects is an important part of a conservator’s work, so I was careful when holding the vase. However, during the condition check, the bottom half suddenly separated from the top. This unfortunate incident prompted my investigation into a fascinating and rare type of glass.
The glass manufactured by Steuben Glass under the leadership of Frederick Carder is known for the wide variety of colors used. This variety is exemplified in the current exhibition, Local Color: Secrets of Steuben Glass. Carder strove to create new colors, coming up with inventive formulas to achieve them. However, in his quest for new colors, Carder sometimes created glasses which were not stable. One such ambitious color attempt was the so-called “Mandarin Yellow”, which was inspired by the color of yellow Chinese porcelain from the Ming Dynasty.1 In attempting to achieve a similar opaque, bright yellow, Carder inadvertently compromised the glass’ chemistry.
There are only about twelve Mandarin Yellow objects surviving to present day.2 It was already known when these objects were created that this color could not be annealed well. Annealing is the process in which hot glass is slowly cooled to prevent internal strains from sudden temperature change. Carder wrote about the Mandarin Yellow recipe in his personal notes from 1919: “Very fine vases in color were made from this but find that it is a glass very difficult to anneal. If vases are made even and thin less trouble.”3 The glass often retained internal stresses due to improper annealing, which once released, would cause major cracking of the object. The former assistant to Carder, Paul Gardner, attributed the small number of surviving examples to the “fugitive quality of this glass”, or in other words, it’s tendency to break.4
The vase which fell apart in my hands was a Mandarin Yellow object. According to a conservation report from 1980, the vase had broken into two pieces at one point but was glued back together with epoxy resin. Now in 2023, the vase separated along the same break again because the previously applied glue failed. Finding out that the old glue was epoxy resin surprised me, since epoxy resin is considered a strong glue. This mystery prompted my investigation into why the glue failed and the object came apart again.
I started the investigation with looking into the composition of the glass, since it can often indicate possible issues the glass may have. Luckily for us, Carder took meticulous notes of his recipes for the different colors he created. His hand-written notes ranging from 1903-1930 can be found in the Rakow Library at the Museum. Notes from 1917 and 1919 give the batch composition of Mandarin Yellow which you can see in Figure 4.5 Portable X-ray fluorescence (pXRF) analysis in the conservation lab confirmed that the recipe in Figure 4 was likely used for the vase.
The glass is a basic soda-lime glass with some additions to produce the desired yellow color and bright shiny surface of the Chinese porcelain Carder was attempting to recreate. Cadmium (Cd) gave the glass a yellow color, and antimony (Sb), which is a fining agent (makes it so there are less bubbles in the glass), helped give the desired shade of yellow. Barium (Ba) was also used to promote the brilliance of the yellow given by cadmium and gave the glass a higher refractive index (makes it reflect more light).6
Barium most likely replaced calcium or lead in the glass mixture. While it helped achieve the desired look, its inclusion increased the thermal expansion of the glass, meaning that it had more stresses to anneal out.7 This is possibly why the Mandarin Yellow objects were prone to breaking. However, the issues with annealing do not explain why the adhesive failed.
Interestingly, a different part of the composition does help explain why the original glue failed. While examining a different Mandarin Yellow vase, I found salts on the inside surface. There is also moisture on the outside surface of the broken vase. These are early signs of atmospheric deterioration (in the past called “glass sickness”). Atmospheric deterioration is a phenomenon where alkali ions from the glass are leached out due to interacting with moisture in the air.8 These alkali ions can then form salts on the surface of the glass. Finding salts on the interior is common with atmospheric deterioration, due to the enclosed space becoming a microclimate where the relative humidity is high.9
Certain compositions of glass are chemically unstable, meaning they are more susceptible to atmospheric deterioration. In the case of the Mandarin Yellow glass, the large amount, 27%, of sodium (Na), which is an alkali ion used as a flux (lowers the melting temperature of the glass), and lower amount, 2.5%, of calcium (Ca), which is a stabilizer, causes an imbalance in the composition. This imbalance makes it more likely that the sodium ions are leached from the glass, since calcium stabilizes the glass by keeping the alkali ions in place.10 Stable soda-lime glass has about 20% sodium and 10% calcium. In the Mandarin Yellow glass, barium was used for its optical properties instead of calcium. Replacement of calcium with barium is known in the glass chemistry world to decrease the chemical durability of glass.11
Since the alkali ions were leached from the glass due to atmospheric deterioration and interacted with the moisture in the air, water stayed on the surface of the broken Mandarin Yellow vase. The current hypothesis is that the moisture on the surface came between the epoxy resin and the glass, causing the glue to fail.
We now know the probable reason as to why the glue failed, but this answer calls into question the stability of other experimental Carder colors. Rouge Flambe is also known to be fragile and prone to cracking, and it is possible that its composition could illuminate problems with the glass. When we know the potential issues, conservators can make the best decisions for the glass, including determining the best environments to keep the objects in to avoid further deterioration. While having an object separate in my hands was unfortunate, it did allow for this research and a better understanding of the fugitive nature of Mandarin Yellow glass. So, while it was not expected, I am glad it happened.
- 1 John A. Shuman, The Collector’s Encyclopedia of American Art Glass: Identification & Values, 2nd ed (Paducah: Collector Books, 2006): 24.
- 2 Carder Steuben Glass Association, “Mandarin Yellow”, https://steubenglass.org/gazelle-gazette/mandarin-yellow-2/
- 3 Frederick Carder, Formula Used at the Steuben Glass Works from 1903 to 1920 (N.p., 1903-1920): 74.
- 4 Gardner, The Glass of Frederick Carder, 77.
- 5 Frederick Carder, Fredk. Carder 1912 [large Black 3-Ring Loose Leaf Notebook of Glass Recipes] (N.p. 1912): 51 & Carder, Formula Used at the Steuben Glass Works from 1903 to 1920, 74.
- 6 Miloš B. Volf, Chemical Approach to Glass, Authorized reprint ed. (English) (Sandy, Utah: Igneous Glassworks, 1984): 430.
- 7 Volf, Chemical Approach to Glass, 275.
- 8 J. J. Kunicki-Goldfinger, “Unstable historic glass: Symptoms, causes, mechanisms and conservation,” Studies in Conservation Vol. 9 No. 1 (2018): 49-50.
- 9 Stephen P. Koob, Astrid R. van Giffen, Jerzy J. Kunicki-Goldfinger & Robert H. Brill, “Caring for Glass Collections: The Importance of Maintaining Environmental Controls,” Studies in Conservation Vol. 63 No. S1 (2018): 149.
- 10 Kunicki-Goldfinger, “Unstable historic glass: Symptoms, causes, mechanisms and conservation,” 49.
- 11 Volf, Chemical Approach to Glass, 275.
- Carder, Frederick. Fredk. Carder 1912 [large Black 3-Ring Loose Leaf Notebook of Glass Recipes]. N.p., 1912.
- Carder, Frederick. Formula Used at the Steuben Glass Works from 1903 to 1920. N.p., 1903-1920.
- Carder Steuben Glass Association, “Mandarin Yellow”, https://steubenglass.org/gazelle-gazette/mandarin-yellow-2/
- Koob, Stephen P., Astrid R. van Giffen, Jerzy J. Kunicki-Goldfinger & Robert H. Brill. “Caring for Glass Collections: The Importance of Maintaining Environmental Controls.” Studies in Conservation Vol. 63 No. S1 (2018): 146-150.
- Kunicki-Goldfinger, J. J. “Unstable historic glass: Symptoms, causes, mechanisms and conservation.” Studies in Conservation Vol. 9 No. 1 (2018): 47-60.
- Shuman, John A. The Collector’s Encyclopedia of American Art Glass : Identification & Values. 2nd ed. Paducah: Collector Books, 2006.
- Volf, Miloš B. Chemical Approach to Glass. Authorized reprint ed. (English). Sandy, Utah: Igneous Glassworks, 1984.
- Gardner, Paul Vickers and Paul N. Perrot. The Glass of Frederick Carder. Atglen, PA: Schiffer Pub. Ltd., 2000.