Greetings all:
I have a question or two…
In my advanced class, they’ve decided that this is the year of
Mokume. So we did simple torch-fired silver/copper laminates last
term, and this term, we’re getting a little more serious. We’re doing
something that’s sort of a combination of Ferguson’s technique with
what I’ve heard is closer to Jim Binnion’s old style. To whit: we’re
using big steel pressure plates bolted together with the stack
between them, sealed in a stainless foil bag that’s been loaded up
with smashed charcoal to soak up all the O2. Firing this in the kiln
for x time at y temp. I’m basing the times and temps on the info in
Ferguson’s book, although since I don’t have the fancy multi-tonne
inert-gas press that he was using, I’ve been doubling or tripling
his times, while holding the temp the same.
We’ve been testing with brass/copper stacks, generally firing for
about 3 hours at 700C, and then letting the bag cool with the kiln.
The initial results haven’t been all I’d hoped. The first billet held
together until I started wedging a knife into the joints, then it
just peeled apart. (Yes, destructive testing.) (If it’s going to
fail, I’d rather it fail before I go to the effort of forging it
down, no?)
So, my questions are these, for anyone who’s done this…
(A) how much charcoal? Since I’m frankensteining Ferguson’s
technique, he naturally says nothing about how to prepare items he
didn’t use.
I’ve been putting in roughly two golf balls’ worth of volume,
pounded up with a hammer into splinters about.2-.4" long. (small, but
not dust.)
These are coming from our bag of dead soldering charcoal blocks. I
knew I’d kept them for a reason… (Packrats of the world unite!)
After the run, there’s still solid charcoal left in the bag. My
belief is that this indicates enough charcoal to keep the O2 in
check, although there was a little discoloration on the outsides of
the billet, and the steel frame. (But I’m not sure that the
coloration was an -oxide-. It could have been something else.) (A1)
Does pounding up the charcoal matter? My belief is that more surface
area must be good, but it’s a messy PITA to pound it to bits. If it’s
not necessary, I’d much rather just toss in a couple of solid block
fragments.
(B) is it necessary to hot-forge the billet as the final bonding
stage? I note that most of the kiln-fired mokume recipes call for
pulling the billet & plate combo out of the kiln right at the end,
and smacking it a few times with a sledge to add enough extra energy
to force the plates to bond more intimately. Ferguson didn’t do that,
but then again, he had that fancy hydraulic press rig. All the
kiln-fired recipes that I know anything about also don’t use the
stainless bag trick. My hope is that the long soak times in a
reducing atmosphere will achieve the same effect without having to
wait around to pound on it at the end.
© I’m basing my temps on Ferguson, but he had that fancy hydraulic
press with inert-gas bonder rig. All my reflexes are looking at 700C
(about 1300 F) as being too low, even assuming that the billet is
under pressure, and held for hours. On the other hand, that’s just my
reflexes. St. Ferguson the Insane, Boy-Wonder of Science, has real
data to build on for his temps, so I’m inclined to run with his data
until I know different. Thoughts?
(Don’t for a second think that comment is anything other than awed
respect. For those of you who know me, the fact that I think he’s
nuts (in a brilliant way) should tell you a lot.)
So, thoughts? Experience?
Regards,
Brian Meek.