The Cambridge Colors: Crown Tuscan

By Les Hansen
February, 2003 - Issue #358

The publication of Henry T. Hellmers' Batch Book of Glass Formulae provided me the motivation to learn more about the production of glassware in general and Cambridge glass in particular. Bill Courter, the Bright Knight of the Aladdin Knights club, published the batch book in limited number. Courter presented a copy to NCC at last year's NCC convention and some NCC members, including myself, also obtained a copy.

I subsequently met with John Boyd of Boyd's Crystal Art Glass, Inc., in Cambridge, OH, who is the fourth generation of the Boyd family to be involved in the manufacturing of glass. John talked me through some of the fundamentals of glass production, and he highly recommended the textbook, Modern Glass Practice, authored by Samuel Scholes and originally published in 1935. The book was revised five times with Scholes as the sole author. However, a final revised edition was co-authored by Charles Greene and published in 1975. This edition is still available from the Ceramic Book and Literature Service (website: www.cbls.com). This 493-page book provides a wealth of information on the challenges of producing glassware.

One of the key characteristics of Cambridge glass is that it is "pot" glass rather than "tank" glass. Cambridge glass was made in clay pots that were arranged circularly within furnaces, and most of the Cambridge formulas in the Hellmers batch book are for raw materials that total 750 lbs to 2200 lbs in weight. On the other hand, the making of glass in tanks offers economy of construction of furnaces and economy of glass production, typically in batches weighing several tons. Pot glass is regarded as superior to tank glass, and glass formulas differ depending on whether glass is produced in pots or tanks. Hellmers began employment with Cambridge in 1930 and immediately developed the formula for Crown Tuscan. His batch book has six pink opal (opaque) formulas with Cambridge listed as the manu-facturer. The first entry is dated April 1, 1930 and is listed with the ivory-colored opals. It is labeled with the name Crown Tuscan and with the notation that it is for both pressed and blown glassware. The five other Cambridge entries are in the pink opal section of the Hellmers batch book with the following dates and notations:

The formula dated 9/8/32 is identical to the formula dated 4/1/30. It is also identical to the formula provided by Hellmers to Courter on August 23, 1973, when Courter quizzed Hellmers regarding the differences in the formulas for Aladdin's Allacite color (tank glass) and Cambridge's Crown Tuscan (pot glass). Hellmers developed both of these colors, but the formulas differ. Past articles in the Crystal Ball as well as information in the Colors in Cambridge indicate that Crown Tuscan was introduced to the public in September 1932, although Hellmers developed this color more than two years earlier in April 1930. Twelve raw materials were used for the original formula (4-1-30 and 9-8-32) for Crown Tuscan: ED NOTE: Shouldn't this be eleven?

Sand 1000 lb Feldspar 250 lb
Soda ash 225 lb Fluorspar 200 lb
Cryolite 100 lb Potash 100 lb
Barium Carbonate 60 lb Zinc Oxide 50 lb
Nitrate 30 lb Arsenic 5 lb
Selenium 4 1/4 lb    

Selenium is a colorant that imparts the pink color to Crown Tuscan. Some additional information on raw materials: Fluorspar (calcium fluoride) is the raw material that causes (in conjunction with feldspar) glass to be opaque. Cryolite is also used in the production of opaque glass, but it is an expensive ingredient that is mined in Greenland.

One of the key features of Crown Tuscan glass is the range of colors. The Colors book states this perfectly: "It is found in a wide range of shades from a dark tan through shades of pink to almost white. Some pieces show streaks that approach brown in a slag effect." However, collectors have noted that a high percentage of the items that have the darker shades are from molds that were used only during the early years of production of Crown Tuscan. In particular, pieces with the Crown Tuscan stamp signature have a higher likelihood of having dark coloration, and these items date to the very early years of production, probably prior to 1935.

Arsenic is used as a raw material to help remove bubbles ("seeds") from glass and to control the coloring effect of iron in glass. Iron is an impurity in raw materials that imparts a blue-green color to glass. Arsenic tends to shift the coloring effect of iron from blue to yellow. It is interesting that Hellmers' notation ("color brownish caused by arsenic") on the original formula for Crown Tuscan could explain the darker color and sometimes slag effect found in some, especially early production, Crown Tuscan items.

Another batch book has surfaced that contains Cambridge formulas, and it has numerous formulas for Crown Tuscan throughout the 1940s. By 1942, the amount of arsenic in the Crown Tuscan formula had been halved and by the mid-1940s arsenic had been almost completely or completely removed from the formula. Also, these formulas from the 1940s have less cryolite (expensive and perhaps hard to get from Greenland during wartime), less borax, and more feldspar on a percentage basis than the original formula. It is becoming very clear that typically more than a single formula was used to produce Cambridge colors over time.

I hate to revive the old debate about the colors of Coral versus Crown Tuscan; however, the notes and alternative formulas for Crown Tuscan (the ones dated 9/14/32 and 9/22/32 have no arsenic) in the Hellmers batch book suggest that care might have been taken to make sure that arsenic wasn't used (to counteract the coloring properties of iron) in the Crown Tuscan formula when making Seashell items. This could help explain why very few Seashell items have a brownish color, but instead tend to have more of a bluish tint compared to some other Crown Tuscan items. The tan, brown, and slag coloration of some Crown Tuscan items is likely the result of arsenic in the formula as well as the presence or absence of iron as an impurity in the raw materials used to make glass of this color.

Next, we will review the formulas for the color called Carmen.