Sid â€” You are right. I had not seen that piece about ruby glass before, and that is exactly the effect I was trying to describe. With the Walsh Mother of Pearl, the opal layer is none too stable, and can start to break up into a tiny crackle effect, particularly on small fancies with heavily worked flared and crimped rims.
I have sorted out three or four examples, and will switch to my black studio* later today for this, but at the moment I am having problems in my white studio with a Webb pale blue rose bowl with citron legs and rim and an impressed Rd lozenge, which also needs the black for the UV shots! Why do I always buy glass which is so difficult to photograph?
Thanks, Frank and Glen, for the iridizing info. I saw that being done on the end of a pontil rod in a muffle oven at Okra, and I have it clear in my mind, as I am sure that Walsh did it the same way.
* "studio" = 2 camping tables, 2 multicoloured Persil non-bio tablet boxes, a sheet of glass, black or white cloth, and a selection of lights. I always include the boxes into the edges of two or three of a series of photographs so that I can check the colour balance.