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| This article was originally published by SNAG as "The Metalsmith Papers" in 1981.
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Lamination of Non Ferrous Metals by Diffusion
Adaptations of the Traditional Japanese Technique of Mokume-Gane
by Hiroko Sato Pijanowski and Eugene M. Pijanowski
We would like to give our deep appreciation to all the Japanese metal craftsmen and artists who have inspired our work; in particular Mr. Norio Tamagawa for his unselfish giving of his precious time and knowledge. In the text a few others are specifically mentioned. A deep thanks to Dr. Cyril Stanley Smith, Institute Professor Emeritus of the Massachusetts Institute of Technology, for his informative correspondence.
Hiroko Sato Pijanowski
Diffusion can also be used to bond metals together, which is the method studied in this experiment. Atoms diffused between the layers of metal and bonded them together, resulting in a single homogenous structure.
This process may be used to join similar and dissimilar metals which are amenable to by conventional welding techniques." Mayer Engel, Materials Engineering, Purdue University
Kuromi-do is 1% of metal arsenic and 99% of copper. It is potentially dangerous to make, but safe to use cold. When metallic arsenic is added to molten copper it will volatilize and produce poisonous gases. We are still searching for adequate safety procedures to make kuromi-do; these should employ a good ventilation system, specific vapor masks, gloves, etc. One suggestion by Professor Harold Harrison of the Physics Department of Purdue University is to melt the copper and add the arsenic wrapped in a copper foil envelope; hopefully the arsenic will disperse and mix with the molten copper before it volatilizes.
Shakudo is the most useful and easiest copper alloy to make. The procedure of alloying is as follows: anneal an appropriate graphite crucible in a gas or electric melting furnace. Add copper flux (available from Paxton/ Patterson, 5719 W. 65th St. , Chicago , Ill. 60638 ) approximately 1/8 ounce per 5 pounds. When the crucible becomes red hot add metal of the highest melting point. If using highly volatible metals, such as zinc, arsenic, lead, tin, etc., to molten copper take the precautions as noted with kuromi-do. When the copper is molten or fusion occurs cover with carbon, charcoal or any commercially available melting fluxes. Carbon excludes the air from the furnace, and also absorbs any oxygen liberated from the metals during fusion. The fused mass should be constantly agitated or stirred with a carbon rod. In the meantime, prepare the ignot mold by lightly oiling or carbonizing with a candle or dirty acteylene flame the interior surfaces of the ignot mold. Prior to pouring, the ignot mold should be preheated to approximately 100 deg. C When the new alloy is at its lowest possible liquid temperature pour into a tilted mold so that the metal flows down the side wall and does not splash; otherwise it might cause blisters or pits in the ignot. If the ignot is thick and rapidly chilled, the absorbed gases cannot escape from the interior and could cause pin holes. Remove all irregularities from the edges and surface of the ignot or later cracks could occur. Planish lightly both sides of the ignot to completely align the crystals. Anneal the ignot. Adjust the rolls with a feeler gauge (used for gaping spark plugs). When rolling use light passes. Place the ignot in the center of the rolls. After each pan through the rolls the metal can be turned over end over end, this will keep the metal flat. Anneal often. Carl Hines, a graduate student in metal at Purdue University , built the gas/air smelting furnace that we used for the alloying. See Appendix A for details of construction, etc.
Diffusion by the Traditional Method
Mr. Tamagawa uses a thick slug of copper approximately 1/3 the total thickness of the layers as a back-up that will become the inside of his raised forms. Also prepare a piece of mild steel the same dimensions as the copper back-up, this will act as a weight; this should also be rusted. Do not touch the surfaces that are now scratch free. Chemically clean in a solution of 5 grams of potassium cyanide and 1.8 liters of water. Wear surgical, acid proof gloves. Rinse in water and dry with a lint-free cloth or paper towel. A standard acid pickle can also be used. Dry on an electric hot plate. Gas stoves are not recommended because the metal might sweat during the drying operation. Brush away any dust if necessary. Stack the metal in one of the possible combinations listed:
copper, shakudo, copper, shakudo, copper .....
Place the lower melting metals between the higher metals in the sequence desired into the mild steel box. Next place the thick iron plate of mild steel on top as a weight and using thick iron wire bind the layers together as shown in Fiq. 2.
The box containing the laminates are put into a hot forge that is started with a low sulphur content metallurgical coal with hard wood charcoal added to produce a reduction atmosphere. The box of stacked metals is heated to the point where the edges start to sweat (about 900 deg. C) removed and lightly tapped with a wooden hammer. If the copper and copper alloys seemed to be diffused; rapidly remove the binding wire and hot forge. If the stack contains fine silver, wait until the mass loses its red color and then forge. Reduce by forging to about 7 men or 5 mm. Annealing after every course of forging. The Pattern is produced by using a chisel called hatsuri-tagane. The following is the procedure in making the chisel and could be applied to most metal carving tools.  Use a piece of water hardened too[ steel about 10 cm to 12 cm in length by about 1cm square.  Bring one end to bright red and hot forge to the shape of square ended spoon or wood gouge (see Fig. 3) and let air cool.  Place the too] steel or nail blank in ring clamp, or small hand vise, brace it against a bench pin and begin to rough out the basic shape.  After the rough filing, switch to a medium no 2 cut file refining the basic angles and shape of the chisel. Take a coarse emery or wet/dry silicon carbide paper, mounted on a sanding stick. and remove all file marks.  Harden the chisel by heating the last 112" of the cutting edge to a cherry red and plunge into cold water. To insure rapid cooling it must be moved in the water to break the insulation of the steam blanket that otherwise will form around it. It will become glass hard. To test the hardness, run a file lightly over the portion hardened; if it skips and does not cut this means the chisel is as hard or harder than the file.  Temper by using a flame concentrated about 1/3 of the length above the cutting edge. Watch closely as the color marches or moves toward the tip or edge. When about 1/4" of the tip has achieved a pale straw color immediately quench into water that should be directly below. If the tip is blue you have gone too far and must reharden, and repeat the tempering procedures. Each of the colors have a meaning: a light gray color means it is the hardest and most brittle; a pale straw color is not too soft or hard, but just right; purplish color means that it is too soft.  If your chisel has been correctly tempered, use a paste polish (Happich-Semichrome) on a strip of leather, for the final stropping and polishing. Put the diffused metals into a pitch block, pitch bowl or large machinists vise. Start to carve through at least three layers using the hatsuri tagane. Remove from the holding device used. Forge out until completely flat. Repeat the sequence of carving and forging one, two or three times more observing the resultant pattern emerging. Continue forging until about 1.5 rem or any desired thickness needed. It is ready to be raised or formed. After the mokume-gane is formed and finished a coloring process using a unique Japanese patina called Rokusho can be used. Rokusho is discussed in Appendix B.
Experiments in Diffusion
The other half was forged out to 2 mm, a piece 7 men x 15 rem, was cut out from the larger piece cast into plastic; sanded, polished, etched and photomicrographed, (BOX) by Mayer Engel, in approximately the middle of the piece. Figure 5 shows a grain growth where layers had been previously; all except the top most layer where oxidation has occurred in some areas.
A gas furnace allows for a controllable atmosphere. A circular chamber with the single burner set on a skewed line provides a spiral flame path which surrounds the crucible for uniform heating. A lid with a swivel hinge provides access from the top and acts as the flue. A chamber 10" in height and 8" in diameter allows for a No. 12 crucible which is capable of holding 36 pounds of bronze.
All exposed brick surfaces should be coated with a super duty refractory cement to protect from brick particles contaminating the melt.
The hinge is two constructions; a steel rod fastened to the steel jacket with a "stop" even with the top of the furnace, and an assembly which fastens to the lid compression ring. The lid and hinge assembly slip onto the rod which extends above the top of the furnace. A turnbuckle is fastened to the top of the lid hinge and a cable run from it to two points of the lid compression ring. This provides a 3 point support and allows for adjustments of the lid to keep it clear of the furnace top. Additional washers are used as spacers between the lower and upper hinge. It is important that the steel jacket be strong enough to support the hinge.
There is quite a bit of leeway in the burner positioning The flame should hit the furnace wall, not the crucible. A good spiraling flame can be seen from above.
copper acetate Cu (CH3C00)2.H2O - 30 grams
The above is dissolved into 750 ml of water (filtered or distilled) and then it is left to stand for a week or more. The container should be glass, plastic or copper. Drain the top water. This is rokusho! To a copper or pyrex container add the rokuSho with 4.5 liters of distilled or filtered water and 20 grams of copper sulphate. Bring to a boil. Grind, long, white raddish known as daikon and add 5 parts of water. Place a large container of water near the solution of rokusho. Remove all fire scale before the piece is to be colored. Boil the piece (if buffed) in water to remove the surface grease and oils. Clean in a strong pickle solution or in a solution of 5 grams of potassium cyanide with 1.8 liters of water.
1. Cover the object with the raddish solution and dip into the boiling rokusho keeping the piece constantly moving for ten minutes. Remove from the solution and immediately immerse in the nearby container of water, to avoid water spotting or from particles of rokusho drying on the surface of the piece.
2. Repeat step one several times until the coloration is achieved. It usually takes 30 minutes to one hour. Copper should turn reddish brown, shakudo a bluish black and kuromi-do a dark brown and any silver surfaces should remain uncolored.
Another solution: copper acetate - 3 dwt; copper sulphate - 2 dwt; water 1 liter. The above is dissolved and brought to boiling. The procedure is the same as the above. Degrease your hands and wash the object in ammonia and detergent soap solution of equal parts. This solution is not as satisfactory in achieving a reddish brown on copper, but will color shakudo and kuromido. After using either of the two above solutions to achieve coloration on an object of mixed metals, apply a coat of bees-wax or any wax that contains no cleaners, by warming the piece on a hot plate, wiping off any excess wax and polishing with a clean, lint free cloth.
About this article:
This article was originally published by SNAG as series of research presentations, which was given at a SNAG Conference, during 1977-1980. Aided by a grant from the National Endowment for the Arts, they were published in 1981 as a single volume called, "The Metalsmith Papers". "Metalsmith Magazine" was being published concurrently.