Hi Denis -
May I ask you a quick question - and I'd welcome just your guess even if you don't know for sure? I noticed in a video by a prominent artist that after discussing the mediums (and mixtures) she uses with the fat over lean ratios the final batch was a 50/60 mixture of Damar and OMS... and then she put a date on the jar. She never mentioned what the purpose of this final mixture was and also never mentioned why she was putting a date on the jar. Do you know, or would you guess as to what significance the date has inasmuch as whether Damar (or this mixture) would go bad over time?
The reason I ask is that after retiring, I have just gotten back into oil painting that I left years ago. Now, I have several bottles of Damar that are 'years' old. Would your guess be that they would still be acceptable to use?