Making your mokume shine

“Mokume Gane pattern formation mimics the erosion of sedimentary layers of rock in nature. Patterned metals become ‘touchstone’ talismans, hollow formed beads, and objects to be worn, including, by the fingers, as a tactile experience.”

— Carrie Adell

The final Details

Putting the final finish on a piece of mokume gane is one of the most exciting parts of the process. It is only after all your labors to create the show stopper, the prize winner, the grant getter, that you will finally see it in all its true splendor (or lack thereof). The proper finish will bring out the grain and texture of the metal, as well as the full color of the alloys you have used.

Texture

“Disc Form IV” by Steve Midgett. 18K, shakudo, 22K, and sterling silver with diamond and rubies.

Acid-etching can be used to remove particular individual metals from the surface of a piece of mokume to create a texture. A variety of acids and etchants may be used to achieve rich surface textures and define areas of color. Etching followed by sandblasting is also good for getting rid of tool marks left from carving. I use a 40% solution of nitric acid for copper-based alloys. You can also use ferric chloride with fine results, but it works much more slowly.

For etching silver, I recommend a 50% solution of nitric acid, and for golds, pure aqua regia. Aqua regia contains 3 parts full-strength hydrochloric acid, 1 part full strength nitric. This is a nasty, fuming, yellow liquid and must be handled very carefully. Aqua regia does not achieve full strength immediately upon mixing and will work a lot better if it has been allowed to sit (in a well-ventilated location) at least 24 hours before using.

To etch a piece containing mokume, use plastic-coated wire or tweezers to carefully lower the piece into the acid solution. Use asphaltum to mask out areas or metals that you do not wish to etch. Check the progress of the etch frequently by removing and rinsing in a water bath to which you have added a little bicarbonate of soda. This will neutralize any acid still on the piece and will make it safe to handle. Examine the piece to determine if the proper depth of etch has been achieved; if not, rinse off all traces of the bicarbonate of soda solution and return the piece to the acid.

You must be careful, especially on thin-layered laminates, that you do not etch them completely away or undercut them so severely that layers start to flake off. Another problem sometimes associated with using acids on mokume has to do with the inevitable fact that there is more than one metal in the acid bath at a time. Due to galvanic action, one metal may lightly electroplate over another. You probably won’t notice this very light plating until you try to patina the piece and not much happens. Contaminated acids can do the same, so I suggest separate acid baths for each combination of metals that you use.

When using all acids you must:

1. Use only storage containers approved for acid.

2. Add acid to water, never water to acid.

3. Wear acid-proof gloves, clothing and face protection.

4. Use adequate ventilation to avoid breathing acid fumes.

Surface Finishes

As a general rule highly polished surfaces do not work well with mokume gane. A reflection on the surface of the metal causes the eye to be distracted from the patterns in the metal. To cut down on this reflectivity, most artists working with mokume put a matte or brushed finish, on their pieces with acid, steel wool, ScotchBrite pad, wire brush, or glass bead blasting. As with all design decisions, the proper finish is a personal one. Experiment with a lot of different finishes and choose the one(s) that suit your eye.

Color

There are a wide variety of metal colors and patinas that can be used to enhance the look of your mokume. Several formulas follow for use with copper and silver-based alloys. There are also many commercial patinas including the traditional rokusho (most of which are for copper alloys). One of the simplest patina solutions you can make is as follows:

1 pint household ammonia
1 tablespoon salt

Immerse copper alloys in a hot, not boiling, solution of this mixture for 5 to 20 minutes. This is an excellent patina for coloring shakudo. More concentrated ammonia may also be used, and it is possible to attain beautiful colors by suspending the piece over the ammonia in a sealed container and fuming for an hour or so.

Caution: High strength ammonia is quite dangerous and should be handled as you would an acid. Like an acid, it, too, will etch copper-based alloys, so be sure to monitor the coloring process carefully.

Hiroko and Eugene Pijanowski recommend making your own rokusho solution to color mokume-gane using the following formula:

6 grams copper sulfate
1 gram table salt
900 ml distilled water

“Islands” by Wayne Victor Meeten. Copper, silver, nickel silver, gilding metal and glass.

They describe the coloring procedure based on the traditional Japanese process:

“To color mokume gane, mix in a copper pan or Corningware (do not use stainless, aluminum, steel, brass, bronze or enameled steel. Working under good ventilation, bring the solution to a boil. To prepare the metal work for coloring, remove all firescale, and de-grease by boiling in water or using a commercially available cleaner; Fantastic-brand is a good grease remover. Clean the piece in a strong pickle solution. If the metal work contains silver, cover it with ground Daikon (Japanese radish), then dip the object into the boiling solution, keeping it in constant motion for ten minutes. Remove from the solution and immediately immerse in water to avoid spotting from water or particles of rokusho drying on the surface of the piece. Repeatedly boil in the solution and rinse in the water bath until the desired color is achieved. This may take from 30 minutes to an hour. After coloring, all surfaces, other than gold, must be waxed and buffed with a soft cloth. Lacquer can also be used as a protective coating.”

Liver of sulfur is also a very effective patina for both copper and silver alloys. My advice with patinas is to make sample metals palettes, including all the alloys you think you will ever use for mokume. Then try as many different solutions and application methods as you can, to find what works best for you.

Now that you know how to color mokume gane, I want to caution you about using patinas on high-wear jewelry items. Patinas are great when used appropriately; it’s when they are used for pieces that receive high abrasion or frequent submersion in all kinds of liquids that you can really get into trouble. Do yourself and your customers a favor and don't rely on patinas to temporarily carry the strength of your design. Remember, you are creating heirlooms and artifacts (right?); be mindful of that as you build them.