The Robert Christopher Company - Creating a Mokukme Ring

How we make a Mokume Ring

The first step is to determine the metals that will be used in the creation of the Mokume ring. In this case the design calls for 14 karat palladium white gold and Platinum enhanced silver. The 14 karat white gold is made with 58.5% pure gold and 41.5% palladium, and yields a nice greyish white alloy. The platinum enhanced silver is 92.5% Pure silver, 5% platinum and 2.5% copper. This alloy gives a beautiful bright white color and exceptional ductility, malleability and tarnish resistance.
And then the molten metal is poured into an ingot mold to create a solid rod. The picture at left shows the solid rod of Platinum enhanced Silver as it is removed from the ingot mold. The 14 karat palladium white gold ingot was prepared the same way.
After pouring and removing the ingot from the mold, the irregular ends are sawed off and the ingots are placed in the pickle (a hot acid bath) to remove oxides and flux from the surface of the metal
Once the round ingots have been poured, they are hammered (or forged) into a rough square to allow them to fit in the rolling mill:
Then the rods are deburred with a small abrasive wheel on a flex shaft machine to remove any imperfections and to create a smooth surface in preparation for the rolling mill. They are carefully cleaned after this to remove any abrasive residue
After the rough square shape has been created with a hammer and the mostly square rod has been smoothed and cleaned, the ingot is rolled through square shaped openings in a rolling mill to create a square rod. Progressively smaller squares are created until the rod is at the correct size
Once the square rod has the correct dimensions, it is annealed. This relaxes the stresses created through cold-working and softens the metal
in preparation for continued rolling
These are the still red-hot ingots of Platinum-Enhanced Silver and 14k Palladium White Gold. They were just annealed to relieve the stress created by cold-rolling them.
After annealing the metal rods, they are again pickled, surfaced with a scotch-brite wheel and cleaned in the ultrasonic before being rolled through the flat rollers on the rolling mill to create a strip
The sheet is rolled progressively thinner and thinner until it reaches the correct size for cutting into the pieces that will make up the billet stack
The strips are cleaned, annealed again, cleaned, pickled, scrubbed with a scotch-brite pad and then cut into pieces for the billet stack
The many pieces of strip that were cut to the same size have been cleaned and are ready to stack in the clamping jig. The jig is made from 1" square steel and clamped together with grade 8 bolts and nuts. The inside of the clamp, where the stack of mokume billet will touch the steel, has been coated in yellow ochre to prevent the fired mokume billet from sticking to the steel.
The pieces of Platinum enhanced silver and 14K palladium white gold are carefully stacked on the clamp using tweezers to keep them clean, as they have been washed and rinsed many times to ensure that there is no dirt or skin oils on them. They alternate: 1 strip Platinum-Enchanced Silver, then 1 strip 14K Palladium White Gold, then 1 strip Platinum-Enhanced Silver, etc..
Then the stack clamped in the jig and the bolts tightened to create extreme pressure during firing
The jig with the mokume billet stack is then wrapped in stainless steel and packed with charcoal. The charcoal will create a reducing atmosphere to prevent oxides from forming when the whole package is heated in the kiln
Then the stainless-wrapped package is placed in the kiln. The tubes on each side are only for support, to keep the clamp vertical
The temperature in the kiln is raised to 1600 degrees Farenheit and held there for 6 hours to permit fusing of the strips
After the billet has been fired for 6 hours at 1600F, it is allowed to cool and the stainless envelope is opened
The billet layers have fused together into a solid mass with 24 layers
To prevent stress risers from forming cracks in the billet as it is worked, the edges are sawn off
The billet is cleaned using a scotch-brite wheel on the polishing machine. This removes scale, dirt and surface imperfections from the metal
The billet is then heated to 900 degrees and forged with a hammer and anvil to make a bar that will fit in the rolling mill
After forging, the metal is cleaned with the scotch-brite wheel again to remove the discoloration caused by contact with hammer and anvil and then it is annealed at red heat
After annealing, the billet is pickled to remove oxides and then forged again to reduce its size. It is then again cleaned, annealed and pickled. Once the billet will fit in the rolling mill, it is rolled through progressively smaller slots to create a long, square rod
Rolling through smaller and smaller openings in the rolling mill until the correct size is reached
The mokume rod is cleaned, annealed, pickled and then placed in a vice and twisted to create the pattern
The twisted rod is then cleaned, annealed and pickled; then the edges are forged flat with the hammer and the the edges are filed to a square
The hammered and filed Mokume rod is then rolled through the rolling mill to create a nice square rod again
Once the rod is nice and square again, it is cleaned and then rolled through the flat rollers to create a patterned strip
The edges of the patterned strip are filed parallel
And then the Mokume strip is put through the convex rollers in the rolling mill to create a beveled edge for the ring
The Mokume strip is then formed into a ring
The edges of the ring are then soldered together
The mokume ring is then given a preliminary polish and is ready for the next step
Another view of the mokume ring, ready for the next step.
Now that the band has been fabricated, it's time to create the bezel setting for the diamond. With the band and diamond at hand, a wax model of the bezel is carved to fit the band and the diamond.
When the wax is carved to the exact shape and size needed, (taking into account shrinkage from the casting process and metal loss due to finishing) wax sprues are added using a heated wax pen
Then the carved wax model with the sprues are affixed to a large wax sprue
Once the wax and sprue is complete, it is placed in a can or 'flask' and filled with investment (a type of plaster)
After filling the flasks with investment, they are covered with a bell jar and subjected to a vacuum to remove any trapped air from the investment to prevent bubbles
The investment is allowed to dry and then the flasks are placed in a kiln and the temperature is increased to melt out the wax and burn any wax residue from the investment
After the complete burnout cycle in the kiln, the flask is removed and you can see that the wax has completely melted away leaving a cavity inside the investment in the shape of the wax. In this case, the cavity is the exact shape of the bezel we want for the diamond
The flask is loaded into the casting machine which melts the gold in the crucible and once the gold is molten and at the correct temperature, the machine spins and the gold exits the crucible through the hole in the side and enters the cavity in the flask, creating our piece
The view through the sight glass into the crucible of molten white gold
The flask just after casting with hot white gold filling the sprue cavity
Once the flask cools sufficiently, the investment is removed and the casting pickled and we have the bezel attached to the sprue
The bezel is cut from the sprue and filed and sanded to fit exactly to the top of the mokume band
Once the bezel fits the top of the ring perfectly, it is soldered in place and given its final shape
The Diamond is then set in the bezel and the entire ring polished and cleaned
The Finished Mokume Ring with Oval Diamond
The ring had a matching gent's ring made of 316L Stainless Steel with a Mokume insert.

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