He said that the failure was probably due to storage at elevated temperature in the distribution chain degrading the product (it's comprised of 3 components, all white powder, and the hardener/activator part can degrade)... he guessed that the hot weather we had earlier in the year could be the culprit and said it had happened once before in their history.
Anyway, while I was waiting for the the response from Polyvine I also bought a small tub of Cascamite from Axminster and some Titebond III from RDG Tools.
I re-backed the boo/Yew primitive using the TitebondIII having first cleaned up the mating surfaces on the belt sander. Of course the belt sander removed some material which means the bow is now more like 100# rather than the projected 115# from the first re-backing.
https://www.youtube.com/watch?v=KlXni0I-KI0&t=4s
The small tub from Axminster actually arrived before the stuff from Polyvine and when I mixed a test batch it seemed the same whitish colour as the bad stuff (I also mixed a test sample of that to compare). I was getting pretty frustrated by now but resolved to be patient and wait for the stuff from Polyvine.
When that arrived I mixed two identical test batches. It confirmed what I'd suspected. The good stuff is beige, the bad stuff is near white. I sent the picture to Axminster who agreed a "non return refund" as I said I didn't want the cost or inconvenience of returning the product. The next day I broke the cured test sample in half to show the how it looked, you can see it has separated into two layers, the bulk having a chalky appearance. The good stuff is homogeneous and beige.
I'd suggest anyone buying Cascamite order it direct from Polyvine.com
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