You, might find that a test for the glass's density is more accurate in determining lead content in an object that has had coloured glass applied ,which can affect the results achieved by the use of a black light ,It is also very a handy test used to help in the dating of early lead vessels ,less lead tending to suggest an earlier date of production.
The density of soda/non lead glass is 2.4 g/cm3 or below, while typical lead crystal has a density of around 3.1 g/cm3 and high-lead glass can be over 4.0 g/cm3 or even up to 5.9 g/cm3"
1. find a container big enough to hold the item so that it can be submerged. Place that container inside another container so that when water runs out of one container it is collected in the one below.
2. Fill the first container so that it just starts to pour over the edge (you need to break the meniscus). Then make sure you have no water in the bottom container. Next lower the glass to be measured slowly into the water making sure you don't trap any air bubbles inside the vessel (I would tie a bit of string round it and lower it in that way)
When the displaced water has run over the edge into the bottom container measure its volume in ml's and use this (along with the weight of the item) to calculate the density of the glass as follows...
weight of item in grams
volume of displaced water
=density in g/cm3
the item displaced (conveniently) 100ml and it weighed 323grams. Therefore its density was 3.23g/cm3,= lead
I am sure its not a 100% foolproof method considering the many different compositions of glass but its pretty accurate for most things
A fun test for all to try . but don't drop anything trying it !!!!!!