- To summarise what I state within my web pages:
The UV checks to separate "Ysart Brothers / Vasart Ltd / Strathearn" weights cannot give any conclusions when using only a Longwave UV lamp (which is what all the standard UV pens / lights are). It requires a Shortwave UV light to determine a difference.
Although some folk have suggested a difference in the Green fluorescence, with a lighter Green for "early" items, I have not found this to be consistent. What I have noted is:
all of Ysart Brothers / Vasart Ltd / Strathearn, show as a shade of Green.
- Ysart Brothers (1946 to 1956) show as a "dusty / muddy" Grey
- Vasart Ltd (1956 to 1964) & Strathearn (1964 to 1980) show as Blue
So the only thing that can be sorted out under UV is that if it's Blue under Shortwave, it's from 1956 to 1980, otherwise it's 1946 to 1956.
(Note that it is still not proven for certain that 1956 was the actual date of change of the glass mix - but it does seem likely that it was then or very shortly after.)
- Although some of the bubbles in a number of these weights may appear to have had a deliberate thought behind them, I am sure that it was not the case. And any "iridescence" showing in or around the bubbles is only an effect of the light and the colour of the ground or nearby canes - again, this is not a planned feature.
But I do agree that even unintended random bubbing can sometimes add a bit of interest to many of the standard daily production pieces of rather average quality