Hi Lynn
Assigning a definite attribute for these makers is always tricky for two main reasons.
1) Ysart Brothers, Vasart and Strathearn were all basically manned by the same makers. Jack Allen, Dave Moir and Vince Ysart being the two most prominent ones. The same style goes through from Ysart brothers to Strathearn And in fact Perthshire paperweights was made up of ex Strathearn workers so its hardly surprising to see similarities in early Perthshire weights!
2) The same millefiori canes were used by all three operations so canes are NOT a good guide. Jack Allan who worked for all three firms went to Perthshire and took with him a very large jar of old canes !
So you first have to look at the equipment used. Ysart Brothers and Vasart DID NOT have a glory hole and once the pattern was picked up it was reheated in the mouth of the fiurnace which is no where near as hot as a glory hole hence it was not possible to get the pattern flush with the ground. So in one of these weights where it pattern is distinctly above the ground you start to think Vasart or earlier.
For most of the time Vasart used to rough grind the bases of their weights. However during the last year or so they started experimenting with firepolishing the bases which gives a shiny base with the bubbling shown on some of your weights
Strathearn had glory holes and always as far as I am aware also firepolished their bases. SO a weight where the pattern is flush with the ground and it has a fire polished base is invariably Strathearn.
So you can see from the above you can get a general idea of the likely attribution by applying simple logic and experience of handling these weights helps a great deal. FOr instance Strathearns tend to have a tidier set up than Vasart.
Kev H mentions short wave uv testing - this is done using a professional instrument NOt a uv lamp used for detecting flourescent stripes on stamps, dud banknotes or so called uranium glass!
I have spoken at length to Dave Moir about the attributions of these weights and much of the above is based on those conversations. Dave worked for these three firms for over 25 years so if anyone can throw some light on how to correctly attribute them, then Dave can.
Hope this helps
Derek