Yes he has (or his heirs have ) patents on the tension setting in
heat treatable alloys see US Patents 5188679, 5084108
Both of those patents expired on January 28, 2009. So anyone in the
USA is now is free to make such tension set jewelry as those patents
protected. Anyone outside the USA (baring any foreign patents which I
have NOT looked for) has always been free to make such tension set
jewelry, just not to import it into the USA. Of course, that doesn’t
let anyone off the hook that infringed BEFORE the expiration of the
patents.
However, one cannot use Kretchmer’s platinum-gallium (-palladium)
alloys as spelled out in patents 5,846,352 and 6,562,158 IF (and most
likely it is so) their maintenance fees have been paid (at 3.5 years
for both and also 7.5 years for the first).
If anyone seriously needs the issues sorted out I strongly suggest
connecting with a good Intellectual Property attorney. Don’t hesitate
to read the patents first but concentrate on reading the broadest
claim’s only (Claim 1 only in both cases), they are very specific so
not just any platinum-gallium alloy will infringe and even such
alloys will NOT infringe if the spelled out heat-treating or Vickers
hardness values are not met.
James E. White