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Uranium Glass(Page 3)To the collector, perhaps the most popular form of uranium glass is the Primrose Pearline produced by Davidson at the end of the nineteenth century (Plate 4). For a time it became a major prop in their business.
The melt not only contains uranium but also arsenic. The latter caused the glass to turn milky/opaque when re-heated at the furnace. Although they held a patent, there is evidence that other manufacturers copied the process. I have examined sixty examples of Davidson’s Pearline glass; the average density is 2.53 g/cc with a range of 2.49 to 2.57 g/cc. This represents a variation of only 3%. It is interesting to compare this with their clear glass of about the same period, which is lower by about 0.06g/cc with much the same range. I can only speculate that the presence of the uranium has caused this small difference. Unusually I find a wide variation of uranium concentration, varying from 0.22% to 1.36% by wt. This is far more than would occur by random or even poor batch control. Moreover, in terms of colour intensity, items range from a pale to a deep primrose. I observe that the palest items have a uranium content of between 0.22% - 0.28% by wt. There then follows a jump to 0.5%, which ranges up to 1.36% uranium by wt. I can only speculate on the reason for this. Perhaps both pale and deep colour products were sold over the same period, but with the uranium content of the deep primrose being reduced to give a cheaper alternative. Davidson also produced this yellow in transparent colour. I have examined examples that probably date between 1910-1920. Their uranium content is about 0.74% by wt and they have an average density of 2.49 g/cc. Unlike other glasshouses, Davidson appears not to have used uranium in other colours. A large number of greens, including all those on display at the Davidson’s Glass Exhibition at Shipley Art Gallery in 1993, have been examined. Only two items were found which contained significant amounts of uranium, i.e. 0.03% by wt & 0.11% by wt. They are a grapefruit dish and a piano insulator. Neither of these was marked but they were identified from catalogues dating between 1928 and 1940. It is difficult to see why, having not used uranium in the bulk of their greens, they should use it for just a few items. Perhaps these were not produced by Davidson but by some other glasshouse from Davidson moulds. We do know that the Nazeing Glassworks did acquire some Davidson moulds and that Nazeing also used uranium after the Second World War. Again, it is a matter for speculation.
The other major glasshouses on Tyneside also used uranium extensively. Greener appears to have made an equivalent of Davidson’s Pearline, despite the patent. Examples are few and far between, but I have examined one item with the Design Registration Number 262018 (Plate 4). This identifies it as being from Henry Greener & Co., 1895. With a density of 2.53 g/cc and a uranium content of 0.62% by wt. it is indistinguishable from Davidson’s Primrose Pearline. Greener, and later their successor Jobling, used uranium for other colours. Two of the original Greener notebooks are in the possession of Sunderland Museum and Art Gallery. These suggest that up to the 1880s uranium may only have been used for the production of green glass but this is by no means certain. The colours Topaz, Canary, Gold Yellow and Primrose, made by using uranium, are mentioned after 1885. However I have found three Greener items in yellow, with Design Registrations between 1867 and 1870. Their densities range from 2.56 g/cc to 2.64 g/cc and the uranium content from 0.19% to 0.26% by wt. It is quite possible that these items were made after 1885 from earlier moulds. Unfortunately I have not yet come across a uranium green of the 1860/80 period.
By the 1930s, now trading as Jobling, the company used uranium in their green and jade non-Pyrex glass (Plate 5), but I have not found any yellow examples. Baker & Crowe in A Collectors Guide to Jobling 1930s Decorative Glass give a formula for the Jade which I would expect to lead to a glass of about 2.60 g/cc density and 0.28% uranium by wt. This is consistent with the few measurements that I have made on their Jade. However the Jobling clear and frosted green appears to have a lower density of about 2.47 g/cc and a uranium content of 0.13% by wt. Sowerby, like their Tyneside competitors, also used uranium. During the latter part of the 19th century they appear to have used it in both green and yellow glass, but the only examples from the 1930s I have found are green. With regard to their 1880’s wares, the yellows have a uranium content of between 0.25% and 0.5% by wt. I have examined only two green items and, although one was much deeper than the other, they had a uranium content of about 0.37% and 0.43% by wt. respectively. Perhaps the most interesting is their “Queens Ivory” range (Plate 6). Sowerby patented their mix, which had 24 lbs of “uranium” in 14 cwt of batch. Allowing for uncertainty about what is meant by “uranium”, this is consistent with the measurements I have made. Nine samples lie between 0.93% and 1.24% uranium by wt., but two other pieces have only about 0.65% uranium by wt. It is difficult to explain these variations unless Sowerby
The Lancashire glasshouses were probably using uranium before the large Tyneside producers. A surviving pattern book from the Manchester firm Molineaux Webb & Co suggests that that the company was producing pressed glass at least by 1851. I have examined six pressed candlesticks, which are illustrated therein (Plate 7). They are all yellow bordering on amber and their uranium content lies between 0.43% and 0.56% by wt. Their densities are 3.3-3.4 g/cc, which probably means a lead content (or possibly barium) of 35% or greater. Other, non-uranium glass from this company, which I have examined, suggests that in the 1860-1880 period the density of their glass was about 2.8-2.9 g/cc. I think it likely that lead content was reduced over the years to keep production costs competitive, in which case the higher leads represent the earlier glass. Almost certainly these candlesticks are not typical of the bulk of Molineaux Webb glass. I have only been able to examine a few items of uranium glass, which I consider, probably originated from this glasshouse in the 1860-1900 period. One is a pale yellow candlestick with a density of 2.68 g/cc and uranium of 0.26% by wt. The others are four green knife rests, all of the same pattern (Plate 7); their densities range from 2.73-2.96 g/cc and uranium from 0.25% to 0.37% by wt.
Text © Barrie Skelcher and The Journal of the Glass Association 2001. |
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