Now it’s time to color our antler kagamibuta bowl. I’ll be soaking the antler first in a hot, but relatively weak solution of potassium permanganate (KMnO4), then polishing to remove much of the color. I’ll repeat this a number of times until I’m satisfied with the color, and, in this case, will follow up with a hot solution of yellow fabric dye to “warm” up the color.
Potassium permanganate, while a garish purple color in water, is NOT a dye. It is, instead, a heavy oxidiser. When it first colors the antler, it will appear a horrible purple, but will quickly turn to various shades of brown, eventually aging overnight to almost black in the porous areas of the antler. This is highly dependent on how much soaks in, hence the repeated soakings and polishings. When I’m finished with the process, I’m hoping this will end up looking like old antler netsuke, by simulating the aging process.
As natural materials age, they typically darken due to oxidation. There are two main sources of age oxidation – oxygen in the atmosphere and light. Both of those are oxidising agents. Potassium permanganate does exactly the same thing, just far more quickly.
Above is my double boiler contraption. It is just a thrift store pot and a glass jar. Do be smart here and NOT use the best pots and pans of She Who Must Be Obeyed, or you’ll end up in the doghouse. Don’t ask how I know this. I’ve warned you, so if Momma gets mad at you, it’s your own damn fault! Also, potassium permanganate IS a powerful oxidiser, and you should not mix it with anything but water. Don’t drink it. Yes, it will stain damn near anything it gets on. It will attack metal, so use a glass jar, not metal. We are using it with boiling or near boiling water, so do not use plastic containers. Things will be HOT, so don’t burn yourself.
This is about 1/24th of a teaspoon (approx. 1/3 of a 1/8th teaspoon measure) of potassium permanganate in 100 ml of water.
Here’s the antler bowl after about a minute of soaking in the hot potassium permanganate solution. I’ve used a piece of string tied to a button for convenience so I can pull the bowl out of the solution periodically, dry it off, and polish most of the color away. Obviously, the harder areas of the antler will absorb less of the solution (and be lighter in color), and the more porous areas will absorb more (and end up darker in color).
I find I like using my Foredom flex shat grinder and ScotchBrite™ pads to remove the outside layer of color (I like the purple colored stuff best for this), but really fine sandpaper followed by buffing with jeweler’s abrasive compounds will work. I would NOT use colored polishing compounds since the grit will end up in the pores of the antler and undesirably tint the antler. I have a white polishing compound that I like.
Above are a series of images of the antler bowl after soaking, along with a set after polishing so you can get an idea of how the coloring process goes. Each set has the bowl as it appears right out of the hot solution (dry), followed by a set after polishing. Each set is separated by a blue outline. The last set in the blue box is after the hot yellow fabric dye. All together, I did about six trips in the potassium permanganate (about 5 minutes each time), and one 5 minute soak in the yellow dye.
The colored bowl with the lid. Now to let it sit for several days to dry COMPLETELY, then I’ll apply a final finish. Since I’m concerned about humidity changes (since the original ivory bowl cracked), I’ll apply a nitrocellulose lacquer finish in the hopes of eliminating at least some of the humidity sensitivity.
I’m going to use my incredibly “high tech” setup to help the nitrocellulose lacquer penetrate a bit better, at least into the more porous areas. Above are the components I use – basically a large glass jar (that seals well), a hand vacuum pump, and a smaller glass jar holding the liquid lacquer. I thinned the lacquer with lacquer thinner, somewhere between 2 parts lacquer to 1 part thinner and 1 to 1. I just need the liquid to be a bit thinner than it comes from the can.
Above I’ve sealed the unit (the bowl is in the liquid – make sure it submerges completely) and pumped a vacuum to about 20 inches of mercury. I’ll leave the bowl in the liquid under vacuum for about an hour, then release the vacuum and leave the bowl in the lacquer for at least another hour. The vacuum only removes air from the porous areas of the bowl, then ambient air pressure (about 30 inches of mercury positive pressure) will force the liquid in. The removed air will help suck the liquid into the porous areas of the antler. The vacuum is only PART of the equation…
Above, you can see a little foam on the surface of the liquid. Some of this is air from the antler, and some is evolved air and vapor from the solvent. Since my system isn’t terribly tight, during the hour of vacuum I’ll pump from time to time to restore the vacuum to 20 inches of mercury.
and here is the finished bowl with the lovely Katsunori shakudo (gold and copper Japanese art alloy) plate, installed at last. You can see more of this netsuke here at Roger Rudolph’s web site: http://ajiarchives.com/pictures.aspx?category=Katsunori
Thanks for looking!