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Mutant Mokume Production


#1

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.


#2

I don’t think the charcoal is the problem. My first thought is that
you are firing at too low a temperature and for too short a time.
Binnion recommends heat sinking at 50-100degrees below the lowest
melting point component of the billet. see

http://www.artmetal.com/project/TOC/proces/forge/mokume01.html

For copper/nu-gold brass, I fire at 1600 for about 8 hours and I get
good bonding. I do pile a lot (more than you) of aquarium filter
charcoal inside the tool wrap, but I don’t think that oxidation is
the problem. If higher firing times & temps don’t do the trick then I
would look to the cleanliness of the metal before bonding and,
perhaps, the charcoal.

Good luck-
Debby


#3

Hi Brian,

Try baking the charcoal for a few hours prior to using at 350 F. This
will drive off any moisture. Also, you may want to spend the few
dollars it will cost for activated filter charcoal (aquarium or pet
store). I’ve always found with mokume it pays to use new, quality
ingredients. Sort of like making an expensive gourmet dinner. But,
bake the charcoal, even if new. Two golf balls is probably enough,
but it’s cheap, and it does not hurt to use more. In the “good old
days”, we’d surround the system (torque plates, bolts, billet) in the
stainless foil with the charcoal.

We don’t crumble our charcoal - just use it straight from the box.
You do need to use the stainless bag for the best bond, especially
using the method you’ve outlined.

Also, torque plate and bolt materials are important - you want thick,
solid plates, and high end (grade 8) hardware.

Invest in Steve Midgett’s book.

Remember, the temps you are using correspond to Ian’s method, not
Jim’s. So do the times. Mokume bonding is a function of time, temp
and pressure. Change one, and the others change - quite closely
related. You are not nearly generating the type of pressure that
Ferguson’s method does, so to make up for that, perhaps a higher
temperature and longer soak. See Steve’s book.

Cleanliness is also critical to this method - much more than it is to
"firebrick" mokume. And materials - make sure you are using oxy free
copper.

As far as bond strength, it will develop in the subsequent reduction
of a billet, provided it is reduce correctly, so fire a taller billet
than you need, and reduce it. It’s not unusual to be able to tear
apart a properly bonded billet in the early stages prior to
reduction. You don’t need to forge the billet while hot with a
hammer. You DO need to trim or file back the edges. From the point of
most (deepest) overlap, you need to cut back bare minimum 2mm, 3 is
better, to expose fresh, clean inside materials. See Steve’s book -
he also recommends soldering the edges, basically making a protective
"cap" of solder at this stage prior to reduction.

Hope This Helps!
Chris
Chris Ploof Studio
508.886.6200 EST
www.ChrisPloof.com


#4

Brian

I do Mokume with the torque plates-bag-charcoal-kiln method although
I am no expert. My feeling is that mokume gane in some ways is a
more forgiving material than many people believe. But there are a
few rules.

You cannot use random materials. All the brass alloys have different
melting and therefore fusing temperatures, for example the brass
alloy #230 called Jeweler’s Bronze which is 85% copper and 15% zinc
has a melting temperature of 1870F or 1021C. Cartridge brass which
is likely but not certainly the brass found at hardware stores or
hobby shops melts at 120 degrees F less than that! I set my
(uncalibrated) kiln at 50 degrees F lower than the melting
temperature of the lowest temperature melting metal in the billet.
In a brass copper stack that would be the brass. Your temperature
seems awful low, but my experience is with my kiln not yours. I also
go for six hours after the kiln has come to temp. not sure if thats
right but so far its worked. I would love to know that the optimum
time and temperatures are but you will get many different answers
because everybody has to adjust things for their equipment and the
particular metal combinations and within that there may be more than
one thing that works.

Next rule, use the same kiln always and place your packet in the
same place. It would be nice if you knew if your pyrometer is
accurate of not, assume it is not and be prepared to adjust your
temperature based on your results. Even if it is accurate, your bag
is resting on the bottom of the kiln where it is a bit cooler. I
used to do some glass fusing and slumping in a kiln and I couldn’t
could’t figure out why the glass kept boiling at first! Duh! So I
set it 100degrees lower from that point, the reality was that it was
much hotter in that particular kiln than the dial indicated, the
temperature table I was using for that particular glass wasn’t
faulty.

I use chunky 1/2 inch torque plates and I would imagine that the
assembly takes quite a bit of time to reach the temperature of the
interior of the kiln so the size of the assembly could affect
results as well. Think of how a cake bakes -from the outside in.

Your next question about the charcoal- I use granular aquarium
charcoal and fill full and pack it down in the bag lightly. I don’t
know it this is optimum.

I don’t forge it due to the awkwardness of the situation and not
having a good workspace to do it in where the kiln is located. I
would prefer to forge the billet a little but since many brass
alloys are hot short (they crack it not forged at just the right
temperature)I would go easy. In fact if anybody knows of any brass
alloys aren’t hot short I would love to know, other than 220 which
is too red. I am planning to work on the hot forging mokume issues
since I do a little blacksmithing and is a direction I am moving
toward-time allowing!but I can tell you if you try to hot forge a
CARTRIDGE brass-copper billet the brass will crack if you push it
very much, You can thump it a little but don’t whomp on it like it
was iron. You need to be able to read the color and I don’t know
what it is for that metal.

You can get some high temperature grease, the kind with granular
copper in it (not aluminum!) and put a little on the bolt threads so
that they don’t get stuck.

I sand all my pieces smooth and clean and degrease before assembly,
a lot of work! could use some shortcuts or advice there myself. Get
it in the kiln right a way to keep oxidization down.

Results may vary
Celeste


#5

Hello Brian,

When fusing brass and copper you can heat the billet up to the point
that the brass starts to melt (but not too much) Ferguson’s
technique relies on a lot more pressure than I use. Success is a
function of temperature, time and pressure. You can increase
temperature only to the point that things start to melt. Pressure is
limited by your equipment.

In my shop I do not use the foil and charcoal method. I use a gas
forge and flux. The gas fire creates a reducing atmosphere and I
coat the outside edges of the billet, after it is clamped with a flux
that is 50% boric acid and 50% borax with just enough water to make
it liquid when it is hot. My billets are pretty big, so they take a
while to bring up to temperature, usually about 15 to 20 minutes.
Then I hold the temperature for about an hour and bring it right up
to the point that the brass starts to weep before I take it out of
the heat and take off the plates. Your question if it is really
nessisary to immediately forge the billet, I believe that it is not.
But I do anyway. I will put the hot billet right back in the fire
when the plates are off and forge it out to about 1/2 the original
thickness before I let it air cool, avoid termperature shocks to a
newly bonded billet. Copper and brass is pretty easy. I do not do any
edge tripping before the forging and I usually do not press or hammer
on the plates before I take them off.

It is important to understand eutectics when desciding how hot you
can fire a billet. Silver and copper sheets will create a new lower
temperature solder-like alloy at the bond, more so if it is
overheated. I DO NOT avvise heating until the material starts to
melt when bonding material that will form lower melting alloys when
combined. In these cases, like silver and copper, it is good to go
with a longer heat soak.

You can see my process illustrated at

http://www.celtarts.com/mokume1.htm

There are lots of ways to make this work.

Good Luck,
Stephen Walker


#6

I have waited to see what others experience might bring forth on
this topic. I find that the more you do something often the narrower
your field of view becomes. So I am always interested to see what
others have experienced. I have fired close to 1000 mokume billets
and have had my share of bad billets. I have blamed my failures on a
wide variety of problems but after many many hours and much research
trying to understand why things did not go the way I planned I have
come to the conclusion that we break far and away more billets after
firing than we make bad laminates.

Something to remember about the directions you find on the web or in
books is that the field of modern mokume gane is new and evolving as
we learn more about what works and what doesn’t. Articles and books
tend to reflect best practice in that authors studio at that time.
There has not been a new book or serious how to article published on
the subject in over 6 years. I guarantee that there have been
advances in how things are done in that time. So look at such
writings as snapshots of how things were done at that time not the
gospel absolute truth.

To get a good laminate you need:

A. Clean metal. This means no grease oil or dirt or gross amounts of
oxides. But do not delude yourself into believing you are preparing
oxide free sheet because the oxides reform in microseconds and often
reach a self limiting thickness in a matter of a couple of minutes.

B. Intimate contact between the sheets and torque (press) plates.
This means flat, parallel faces, even thickness sheet. You can
flatten the stack somewhat by using a press of some kind to bind it
when tightening the bolts but there limits to what you can get away
with here so the closer the sheets are to being flat, parallel and
even thickness the less problems you will have. The torque plates
need to be at least flat on the faces pressing against the billet so
either replace them after each firing or grind or machine flat before
reuse. Unless you are using exotic superalloy torque plates even
thick (1") will noticeably cup after each firing ( check them with a
straight edge if you don’t believe me). This cupping will allow you
to capture a perfect air bubble in-between the sheets while having a
nicely bonded edge all the way around the billet. Compress the stack
and plates and then tighten the bolts on the torque plates. A
hydraulic press is nice but not necessary for this, a good 4" bench
vise can apply enough pressure to achieve the necessary contact. Too
much pressure can actually increase your edge losses if you apply so
much that the sheet starts to plasticly deform. Hot presses like Ian
Ferguson’s are nice but not necessary, and most importantly do not
lead to better billets. It will however give you a greater yield per
billet because you will have less material to remove from the edges
which is especially good when working in gold.

C. Keep oxygen away from the metal while firing. While the small
amount of oxide that forms at room temperature on most metals will
not greatly effect bonding, large quantities will definitely mess
things up. The rate of oxidation and thickness of the oxide layer
increase with heat. A second problem with oxygen is that it is quite
mobile in the metal crystal lattice due to it’s much smaller atomic
size. It can easily fit between the atoms in the metallic matrix and
it will reduce the motion of the metal atoms hindering their
diffusion and therefore greatly limiting the bonding of the laminate
resulting in a failed billet. There are many ways to deal with the
oxygen problem but charcoal in a stainless steel foil bag works quite
well and is easy to do. I have used many types of charcoal from
Kingsford briquettes to laboratory grade activated charcoal. They all
work, Chris’s suggestion about baking the charcoal to remove water is
a good one and will result in a cleaner less oxidized billet. Steam
is a very powerful oxidizer and it is best that you not have any
water vapor in the bag. As for how much charcoal do you need, you
want an optically dense barrier of charcoal surrounding the stack.
You want to make sure any oxygen atoms will strike a piece of
charcoal on their way to trying to get to the metal stack. Anything
less will allow for some oxygen to get to the laminate.

D. Firing times should be as short as possible, 1-2 hours at
temperature is more than adequate. If you have clean metal in
intimate contact 15-20 minutes at temperature is enough. Longer
soaking times lead to larger grain (crystal) sizes and weaker metal.
The best way to know how long your setup takes to reach your selected
firing temperature is to attach a thermocouple to a dummy billet in
your torque plates and measure the time to reach firing temperature.
Then add your soak time to that. After your soak time remove the
billet from the kiln and allow to cool in air. furnace cooling will
lead to in effect longer soak times and larger grain size.

E. Adequate temperature for the metals being bonded will depend on
how much pressure and how much time at temperature and metal
preparation and atmosphere. A maximum temperature is just below
melting point for the lowest melting alloy of the metals present in
the laminate pairs. The minimum will be approximately 50% of the
solidus temperature of the highest melting point alloy in degrees
kelvin. For example for silver and platinum that temperature would be
886 K or 1136 F but your metal preparation, pressure and atmosphere
better be perfect if you want to bond those two at such a low
temperature.

So with all the above if you do not have a closed die hot press like
Ferguson’s the two things you can play with are temperature and
time. You are better off trying for higher temperatures for shorter
times rather than vice versa. To keep the grain size down as much as
possible.

Do not expect high bond strengths from material that has been
laminated but not forged. It is not unreasonable to expect to be
able to peal the laminate apart fairly easily if it has not been
forged. The bond strength is developed from working the laminate
either hot or cold. Hot forging is much safer to the laminate but
cold working can be done carefully with adequate annealing.

So for an example I laminate copper and cartridge brass (C260) at
1450F for 1-2 hours at temperature with a hot forging reduction of
25-50 % at 1450 -1500 F forging temperature. Many copper and brass
alloys will work fine with these times and temperatures.

Remember it is easy to break a billet in the initial forging, bond
strength increases with proper working of the laminate.

Regards

Jim

James Binnion
@James_Binnion
James Binnion Metal Arts


360-756-6550