Pretty sure those weren't made by Burt Co. ..... who incidentally never used lead in their clay formula.
If Burt Co. never used lead in their formula, I wonder who the first chip manufacturer to use lead in their formula was? It may have been
TRK small crowns, which I believe they started producing in the early 1960s. I don't know if the much older
TRK large crowns had lead in the formula. I think I read an analysis of the
TRK small crown chips years ago that found that they had more lead than any other chip produced, and were the most dense clay composition produced. They are slightly smaller than Paulsons, but weigh about the same.
The Burt Co. chips may not have lead in the clay formula, but they did weigh some of their chips with small flattened lead pellets. These can sometimes be seen if the inlay comes off. Many years ago a dentist (Dr. Allan L Myers) wrote an article about how he used his dentist x-ray to x-ray his Las Vegas casino chip collection. He found Christy Jones Hat & Cane chips had lead weights, but Paulson Hat & Cane did not. He also found Horse-head Left, and H mold chips with lead weights, I have noticed several other chips molds made by Burt Co. with some type of extra weight. I believe that customers could choose to have un-weighted, weighted, or very heavy weighted chips.
Below I have a picture of a weighted Willis advertising chip (11.5 grams) on the small key mold, and their "Tri-Heavy Weight" chip, weighing in at 13.5 grams, on the large key mold.
Sorry, don't mean to hijack the thread away from 39mm Paulsons.