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Saturday, February 2, 2013

Mokume Gane

Mokume-gane is a Japanese multi layered alloy of contrasting metals, copper and nickel, different colours of gold, silver, titanium, brass and bronze amongst others, which can be manipulated to form patterns. Translated, it means burl metal. Here, I have a copper-nickel mokume piece that will eventually be used as a handle scale. In essence, it is a non-ferrous damascus allow.

Making mokume is in theory very simple. Place alternating layers of metal atop one another, heat, and apply pressure. That, however, when drawn out into a sheet or bar will not show the pattern until it is manipulated by carving, drilling, twisting, and folding.

The first step is stacking the layers. This will be a 16 layer billet. Coin mokume is a simple, easy introduction to the principles. US quarters and dimes are clad in cupronickel shells, which make them easy to fuse. Additionally, coins do not need any flux to fuse, which removes an important variable from the process.

To hold them together, I bent a bracket in a U and slid the coins inside it. While this will keep them aligned for the time being, when they are placed in the forge the metal will lose its ability to keep pressure on the ends, so I also wrap it in wire to help contain them. It doesn't have to be pretty- it will all be hammered in a moment anyway, so as long as it stays together it will work.

This is the tricky part. The objective here is to keep it in the forge just long enough to bring the entire stack to a uniform temperature and hit it once squarely with the hammer. Too low, and the inner layers will not fuse. Too hot, and the copper will begin to melt. Copper has a lower melting point than the nickel by about 700 degrees (F), so that is the determining factor.

A way to gage the temperature is to watch for the edges to 'sweat'. Beads of copper will begin to form as the cupronickel shell melts. Any more, and it will all run out leaving behind the nickel or homogenizing  into a nice (but unwanted) yellowy bronze NiCu bar.

If you have a pyrometer, great. Set it in the forge or other heat source and wait for it to reach the proper temperature (different for every alloy) and wait a little while for it to become uniform. Otherwise, sit and watch. The change from cold to melting can happen more quickly than should be allowed, but be ready to grab it and hit it with the hammer.

This is still too cold. You can see by the way the edges of the layers (read, coins) are still nice and crisp. To my eyes, the billet will begin to swell and bulge slightly just before it is ready, and the spaces between layers will disappear because they cannot support their own weight.

That's better. A little hard to see, but the layers are flat upon one another and there is a little flaring to the edges. At this point, I left it in for another minute or so and grabbed the tongs and hammer.

When it was up to temp, I took it out swiftly and set it on the anvil, hitting it ONCE. Two reasons for this. One, because it cools off quickly with all that thermal mass below it (the anvil). Copper is an excellent conductor, and will take/release energy far more quickly than iron. Two, because much more than that and it will deform more than it can handle at this state of partial liquidation. Copper and nickel do not expand the same under the same amount of force, especially when the copper is near melting. Hitting it too much before it is fused will cause delamination, leaving you where you started.

After the first round of heating, it can theoretically be taken out of the wire/clamp contraption, but I usually leave it in for another heat or two. After the first, put it back in the fire and wait for it to climb back up to temp. Similar thing with round two. Hit it a few times, firmly but not too aggressively, straightening the stack if it shifted slightly (which it probably will).

The best way to check if the billet stuck is to take it out, let it cool to air temperature, and drop it from a few feet onto something hard, like the floor or anvil. If it breaks apart, then, amazingly, the welds did not stick. If it holds, then it probably did. I say probably, because there can be inclusions and partial welds, etc. With ferrous demascus billets, I like to check the quality of the weld by suspending it from a string and striking it with a wrench or something. If it rings nicely, like a bell or chime, then it is very probably good. If it sounds dead, then there is a failure somewhere. A similar principle applies here, although it is more difficult with softer metals in smaller sizes.

When the welds are all fine and strong, I let it bake for a few minutes before beginning the work drawing it out. Iron is the odd metal of the bunch. It likes heat to be deformed, and a long, slow decline in temperature to anneal it. Most everything else is just the opposite, copper and nickel included. Hammer them cold, and quench to anneal. Do not deform them too much, or the layers will delaminate and split.

This is what the stack looked like after flattening. At this point, it is around a centimetre thick. I cut this in half, making two semicircles that I squared and made into rectangles. Up until this point, everything is essentially the same.

Switching to a different, smaller billet, I'll show what can be done to the pattern and finish. A flat puck, as the one above is, is far from interesting. Clean off the scale and it will look about the same. The edges might show rings, but other than that it will be only one surface of nickel or copper.

This ugly thing is a billet of dimes, about fifteen tall and hammered to around the same, 1cm thick. This illustrates the end behaviour. Cleaned up and smoothed out, it shows the number of layers in contrasting nickel and copper. Sort of.

The copper is muddy and the nickel less than bright. More on that later. The end face, however, is what will be manipulated.

On its own, this is less than interesting. A little nickel showing through on the edges and top, but nothing special. To fix this, it's time to make it ugly. I filed grooves in an X across the face (you can see it in the picture before this one) that cut through about three layers. Intuitively, the thicker it is, the deeper they will need to go to produce the same effect, relative to a thinner billed of similar layer count.

When the layers show through, hammer it flat again. Preserving the character and making it smooth, this can be done as many times as there is thickness to reduce.

Same pattern, but flat now. Drilling a few holes into the surface, and flattening again, it looks like this.

Notice that while there is a semi random pattern, it still looks nothing like the first picture. Now it's time to add the chemicals.

Many commercial products exist to help patinate copper and other things, but in the spirit of doing everything by hand, I decided to stay away from them. For one, this way is cheaper, and for another, it is more exciting. Well, maybe not, but it certainly adds and element of uncertainty and unexpectedness to the result.

The two things that are most important are ammonia and salt. I also experimented with muriatic acid, although that did not do much for me. A third element, although not a chemical, is heat. I achieved some beautiful heat patinas, but they are far from durable. Over time, they lose lustre and fade to natural patina. So with that, here are a few things I tried.

Note- all of these pictures were taken in the same lighting and camera settings.

 1- The original piece of mokume, sanded to 240# and nothing more. The contrast is poor at best and reflected light makes it difficult to see any pattern at all.

2- Heat patina. This is after holding it under a torch until rings of colour begin to wash across the nickel layers. It is easy to heat it too quickly and lose the patina altogether. If this happens, cool it and start again. I stop when I see the straw yellow begin to form, and wind up with mixture of yellows, blues and purples with the occasional green.

3- Washed with acid. Although it brightened the nickel, it killed the heat patina and made the copper blend with the nickel. I used a rag dampened with a little muriatic acid, wiped the face, and left it at that.

4- Salt and ammonia. Similar to the acid, I dampened a rag with ammonia, but sprinkled salt on it where the mokume would sit. Leaving it there for around 3 hours, it came out like this.

5- Second heat patina. This dulled the copper and did not do anything for the nickel. To cool these, I quenched them in water. Later, I tried quenching them in other things but that did not help. The quenching helps retain the colours in the nickel.

6- After finding the muriatic acid too aggressive, I tried a wash with vinegar, to similar results. The contrast is better, but the copper is still a dirty brown  and the nickel faded.

7- Round 2 with the salt and ammonia. Notice the flecks of blue on the left ad top right. These are all that remained of considerably more, but the rest flaked off. The contrast is much better, although the copper patinated too evenly excepting the blue.

8- Another heat patina. The copper really brightened up during the quench, and most of the colours stayed in the nickel. However, the dirty spot on the left and bottom right are no good. In person, the copper was more yellow and the nickel had a neat shimmering effect that changed between blue, purple and green.

9- In the spirit of keeping the colours without the dirtiness, I heated it a second time and quenched it instead in a solution of salt dissolved in ammonia. Strangely, it is nearly the opposite of the not heated salt and ammonia patina. The nickel is darker and the copper lighter.

10- For no other reason than to see what happens, I heated it again and this time quenched it in dilute acid. As expected, it brightened the nickel and copper both, yet this time did not muddy the crispness of the layer lines.

11- In the previous quench, the colours did not stay through the quench, but the surface was prepared nicely for a normal heat patina. This is the last heating, then cooled in near boiling water until dropping to room temperature.

Traditionally, I use mostly a plain ammonia and salt patina, watched carefully and buffed after extraction. There is an endless number of things to produce a patina, and the more I experiment with other things like garlic and bleach and saturated sawdust, the more bizarre results I find.


  1. John,

    Thanks for the great write up on Mokume, especially taking the time to explain the different patination techniques you tried. I appreciate your efforts, and will be looking over the rest of your blog, and recomending it to my son.

    Best regards,
    Albert A Rasch

  2. i just have a question regarding the years of us quarters and dimes that can be used.

    1. Any dime post 1965 is made of 75% copper and 25% nickel (pre 1965 are 90% silver and 10% copper)
      From the same Coinage Act of 1965, quarters have been mostly cupronickel since then, although not exclusively. It is safe to assume that if you have a post 1965 quarter, it will be 91.67% Copper and 8.33% Nickel. An easy way to check is look at the edges. You will be able to see the knurling has revealed the layers of copper, if subtly. It will appear to be slightly reddish in colour.

  3. Dear sir
    How we check the thiknes of different materials. If the melting point of copper is 1200& the melting point of nickel silver is 900 how we check the material quality .

    1. To fuse the materials together, you do not need to be at the melting temperature (which would be a bad thing, as the metals would turn into a pool at the bottom of the forge). To weld/fuse/otherwise join the different materials, you will need to be below the lowest melting point. Since there is a wide range of material combinations, I cannot say what that temperature is for a given billet, so I would recommend trial and error mixed with a bit of caution. If your temp is too low, nothing bad will happen other than a bit of deformation in the materials, so you can always increase the temperature as you go until you have the welds take. Hope this helps you!