Laminating a billet is typically a one shot deal. I am afraid you
will need to send it back to the refiner. The success rate of
"fixing" bad billets is so low that I will say it almost never is
almost never worth the time that the effort takes.
Eight hours is an excessive firing time. We used to do those long
firing times but they tend to be detrimental to the success of the
billet from excessive grain growth.
Palladium and gold form intermetallic crystal structures in the
1250F range, intermetallics are brittle. This may be your problem.
Less time, higher temperature for that combination.
And for your success with shakudo and 22k, they are so easy to bond
that if you had problems with them I would be concerned about
serious contamination problems in your process.
James Binnion Metal Arts