I think this paragraph would be better as the third one to keep the historical info together. What do you think?

Paste imitations have been found in archaeological diggings and collections from over the past 2000 year. First as cabochons and beads later as faceted stones as well. In 1674 an English glass maker, George Ravenscroft (1618-1681), patented a new glass: lead glass. This glass was made with a higher lead oxide content and had a higher Refractive Index (RI) then before. It was a brilliant glass with a high dispersion. All kinds of varieties of composite stones involving paste have been brought on the market. One scheme being more cunning then the other. Paste gemstones can be recognized fairly easy by gemologists that look for gas bubbles, swirly texture and singly refractive stones with a certain range of RI.

(Tim) Absolutely true, it's been changed...