Mokume gane still it will not bond

A question for you mokume artists out there? I have a billet that
has fused except for the middle section it is 18 Kt green 14 kt
palladium white and 14 kt rose. the section that has not fused is 18
kt green and 14 kt white and is dead center of the billet all the
other layers have. I have fired this 3 times after thoroughly sanding
and cleaning the surface, twice @ 1225 deg F for 8 hr and once @ 1525
Deg F for 3 hr and still it will not bond, is there any thing that I
can do to promote these pieces to fuse and will it hurt the metal to
keep firing it? The rest of the layers seem to have fused solid and a
prior billet the same dimensions of 22 Kt and shakudo gave me no
trouble. Any advise would be greatly appreciated

Thank you in advance James Kallas

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
James Binnion Metal Arts