Copper and Brass Raindrop Mokume Gane

As a knifemaker, I like to use interesting pieces for guards and bolsters on the knives I make. One of these interesting materials is called mokume-gane (moh-kum-eh gan-eh). It is a traditional Japanese technique of layering metals to produce a contrasting wood grain effect. The resulting material is beautiful and can be used for jewelry and a variety of metal art.

The idea in a nutshell is outlined in the graphic. Alternating layers of thin copper and brass are compressed and heated until they fuse together. Then the shaping of the product will reveal a grain effect similar to the way that growth rings on wood appear.

For the mokume-gane shown in the photo, I used copper and brass sheet to make up the layers, although other metals can be used such as nickel and silver.

There is a certain amount of skill and some specialized tools required to make this, but I will offer substitutes to make it easier to accomplish in the typical garage. Please note this process deals with high temperatures and grinding of metals. You will require, standard PPE such as safety glasses and welding gloves so be safe.

MATERIALS

The materials needed to get started are:

• 1 sheet of brass, 0.015" thick, 4" x 10". (hobby store: K&S 252)
• 1 sheet of copper, 0.025" 4" x 10". (hobby store: K&S 259)
• 1 tsp borax
• Scotch-brite pad
• Variety of sand papers
• Acetone or alcohol

TOOLS

If you don't have a fully outfitted shop, you can find suitable replacements as noted.

• Aviation snips (metal cutting bandsaw will work too)
• Hammer
• Small anvil (back of your vise will work)
• Drill
• 5/16" drill bit
• Paint brush
• Permanent marker
• Ruler
• Belt sander (rasps and files work too)
• Forge (see note below)
• Hacksaw
• Wrench set
• Homemade mokume-gane press as outlined in Step 2 - Clamp and Flux

Note: If you don't have proper forge, you can make a two brick forge with a propane torch and two firebricks.
Point your favorite search engine to "2 brick forge" for lots of examples.

More details can be found on my Knifemaker's DIY Resource blog: http://dcknives.blogspot.com/

Best wishes,

Dan

Layout

In these steps, one has to mark out the copper and brass and cut it, clean it and stack it. There will be 20 pieces in total or as we say "20 layer mokume."

The sheets that I have are 4" x 10" (100 mm x 250 mm) and that makes 10 squares around 2" x 2" (50 mm x 50 mm). I used my most-handy permanent marker for layout.

Clean

If your metals are dirty, oxidized, tarnished or for whatever reason not clean, scrub them with a Scotch-brite pad or give them a light sanding with some 220 grit sand paper before cutting the squares. Clean both sides until shiny. It is much easier to clean as one big sheet rather than trying to clean 10 small pieces.

Cut

To cut the pieces I used a metal cutting bandsaw. As the metal is fairly thin, I would think a good set of aviation snips (tin snips) would work for this.

I wiped the surfaces with acetone and a clean shop towel. We don't want ugly fingerprints or permanent marker left on the metal.

Clamp

For clamping the stack, I constructed two steel plates similar to the drawing. It doesn't matter a whole lot how thick the plates as long as they don't flex too much. I used 1/4" (~6 mm) and clamped with 5/16" NC bolts. If you are metric, something in the 8 mm size would work. The bolts have to be long enough to get the nut fully on. I found that having at least one bolt longer would allow me to attached a handle to the press. This will come in very handy later.

Once your stack is nicely pressed in the center of the plates, tighten the bolts. You want a good squeeze, but don't overdo it and snap the bolts.

Now the Flux

For flux, I used two teaspoons of borax in some clean water. Mixed and brushed on with a new artist's paint brush. Apply flux all the way around the outside of the stack. This will prevent oxidization of the metals and reduce the risk of having a bad weld in the layers.

Using one of the longer bolts, attached some form of handle. I had some scrap bar stock with a hole in it. Use one more nut and lock it on.

Safety Note on Forges

A propane forge is a wonderful and potentially dangerous thing. There are many risks associated with running a forge from severe burns, to carbon monoxide poisoning, to an explosion. Please understand all the safety risks associated with your forge. Use in a well ventilated area. Zinc fumes can cause "metal fume fever", which is probably not the best thing for you.

Start the forge and let it get up to temperature. Put the stack in the forge and rotate it around. Like cooking a wiener at the camp fire. We're aiming for even heating that goes all the way through the billet. You need to stop heating the billet as soon as you see the brass starting to sweat on the edges. The whole billet with be an orange-yellow color.

DO NOT OVERHEAT! The brass will liquefy and run out from between the copper, effectively ruining your mokume-gane.

Side note:
Copper melts at around 1080°C (1976°F) and yellow brass (which is an alloy of copper and zinc) has a melting point around 930°C (1710°F).

Cooling and Disassembly

In the photo sequence you can see the billet is cooling, yet is still a red color. It will take good amount of time to cool. Let it cool slowly. Give it at least a half hour and check the temperature. If it needs longer, the wait it out.

Donning some welder's gloves you can start to take the press plate apart. I didn't have any luck undoing the nuts. I tried some lubricant, but gave up on that and hack sawed the bolts off.

Partial Holes

To make the raindrop pattern, a series of partial holes are drilled. These can vary in depth and diameter. I went with a straight 5/16" drill bit and drilled a sort of grid. The depth of the "dents" ranged from 1/8" to 3/16" (3 mm or 4 mm). Really anything goes here. Just don't drill too deep.

When are holes not holes?
When you pound them out with a hammer!

After drilling the billet with random dimple, heat the billet in the forge again. This time take it to red hot. With a hammer and anvil, pound the billet flat. This brings the layers from inside the holes back up to the surface. I repeated this process two times.

Whoa Nelly that looks ugly! But there is still more work to do. Those little dents in the surface will be ground out in the next step.

For grinding I used a belt sander. A 60 to 80 grit belt smooth the surface and take the dents out. A rasp or coarse file will do the job too, but slower than the power sander.

As always, use your respirator when grinding.

Once the dents are gone, move over to the workbench and some wet/dry sand paper and work the finish up. In the photo I am using 120 grit wet/dry automotive sand paper. A squirt of water helps greatly here as it lubricates and cleans the swarf away. Chunks can cause scratches to appear so squirt away and sand until the scratches are gone.

After the 120 grit sanding is looking good, move to a 320 or 400 grit. With each grit the raindrop pattern begins to look more and more beautify. This is a really satisfying thing.

Once the 400 grit sanding looks good. Some buffing on a buffing wheel with black abrasive compound really brings on the shine.

This piece of mokume-gane will make four bolsters for knives in the future and adds another handmade dimension to my craft.

I hope that you have enjoyed this Instructable.
Please let me know how it worked for you.

Dan