Metal Musings Blog

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.

Above are top and bottom views of the finished kagamibuta netsuke bowl, after allowing the lacquer to cure for several days.

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!

Above, I’ve installed the hand turning tool rest on the cross slide of the lathe, and begun establishing the outer curve of the bowl with small hand turning tools.  I repeatedly STOP the lathe and hold the original ivory bowl nearby, and sight down the edge to make sure I’m matching the curves.  Incidentally, it is much more difficult to make a matching replacement bowl than an original bowl!  An original only needs to look nice, while a replacement must be the same as the original.  A much more finicky process…

With the top half of the outside curve finished, I reposition the tool rest and begin turning the interior.

Above are the original bowl and the replacement antler bowl.  Looking pretty closely matched in shape.

More of a side view.

And two views without the lid.

Here I’m sanding the inside and top half of the outside of the bowl.  These are 300 grit and 400 grit sandpaper strips (the two narrow ones), and emery polishing paper.

A little closer view.  Can you see the shine beginning to show?

Now that I’m satisfied with all of the curves and smoothness of the finish,  it’s time to remove the bowl from the rest of the material.  My little parting tool won’t cut all the way through, so I’m pressing my trusty jeweler’s saw into service.

Above are the original ivory bowl and the replacement.  Note that the bottoms don’t match.  I’ll now remount the antler bowl with the bottom out, and finish turning.

Here, I’ve remounted the bowl on a three jaw chuck (which is self centering) so I can turn the bottom of the antler bowl.

First, a little facing cut to make the antler bowl the correct thickness.

Above, I’m sighting down the original curve to make sure I’m duplicating it on the antler bowl.  I do this quite a few times, often marking on the antler with a pencil and cutting just a little bit at a time until it’s correct.

A view from above.

And a view from the bottom.  Turning and initial polishing is finished.

And a view from the side.  Pretty close match, even if I do say so myself!

And, above, through the magic of Adobe Photoshop, both bowls with the kagamibuta lid.  I’m pretty happy with it!

Above, I’ve drilled the proper sized hole through the antler cylinder.  The cord that connects to the lid will eventually pass through here.  Incidentally, using a metal-cutting lathe for these parts of the bowl-turning process really helps with accuracy and speed.  As you might surmise, a lathe that can cut steel cuts through wood or antler like butter.

Now I’m ready to cut the recess in the top of the bowl that the plate will fit in, leaving a little flat shelf so it will lay nicely.  I’m using a carbide boring bar to carefully bore this recess, being VERY careful to measure both the proper width as well as the proper depth.  It’s easy to cut a little more if necessary, but what you remove can’t be put back.  With that in mind, by the way, I cut a little more antler than I really have to have, so I could make a mistake here, cut it away, and start again.  I try to live by the principle of “Graceful Degradation.”

Also, I’ve found antler to be very abrasive, so carbide cutting tools are a great help if possible.

Above is the finished recess for the lid.

Now I need to remove as much waste material from inside the bowl as I can.  I’ve carefully measured the original ivory bowl, and marked (with a felt tip marker) the depth I need to cut the hollow interior to.  I’m being careful to remove as much waste as possible, but leaving enough material for the final turning.  Remember that the bottom (and interior) of the bowl is rounded, so take that into consideration!

Above is an end view before interior waste removal.

The same view, with my nice little depth measuring tool.  I don’t remember where I picked this up, and there isn’t a brand label on it, but it is VERY useful.

Here is how it all looks with the waste removed.

The original kagamibuta bowl and lid.

The lid test fit into the replacement antler bowl cylinder.  Just right!

Above, I’ve installed my parting tool onto the lathe cross slide.  I’m going to partially cut a groove into the antler cylinder, marking the bottom of the bowl and providing a little free space for my hand turning tools later.  I’ve marked the cut with a pencil, using my handy little depth measuring tool.

And an end view of the same.

Above, the groove cut, leaving about 5/8ths of an inch in the center.  Don’t cut too far in and weaken the cylinder or you may get vibration and not get smooth surfaces.

I was approached by a client to turn a replacement bowl for a lovely kagamibuta netsuke that had a cracked original ivory bowl.  In my life with netsuke, I’ve found that cracked ivory, especially kagamibuta netsuke bowls, is very common.  It’s my view that ALL ivory will eventually crack, sometimes catastrophically.  Ivory, being such a dense material, but also quite porous, moves with changes in humidity, and eventually I believe all of it will develop at least small cracks.  Now don’t let this turn you off of lovely ivory, because in most cases I’m talking about cracks occurring over many decades, and perhaps centuries.

Above is a kagamibuta netsuke of mine.  This one has a plate or lid of carved porcelain with a celadon glaze, and a deer antler bowl.  Kagamibuta means “mirror lid” in Japanese, and commonly the lid or plate was made in metal.  You can learn more about netsuke here:  http://www.netsuke.org

Kagamibuta netsuke are one of the several common forms of netsuke, and came about mainly because of changes in Japanese laws that prohibited the carrying of swords.  Those metal artisans who made all of the astounding samurai sword “furnishings” suddenly needed jobs, and kagamibuta netsuke took up some of that slack.

I had several choices to make this kagamibuta bowl from, and I chose naturally-shed moose antler (most deer shed their antler every year, so no animal needs to be harmed!).  Above is a cross sectional view of a nice piece of moose antler, cut through the “palm” of the antler.   Like most deer antler, moose antler has harder outer margins surrounding less dense and porous interiors.  The main difference between antler from different deer species is how much of the outer part is hard, and how much of the interior is porous and soft, although nutrition of the animal can also play a large part in this.

Above is a cross section through the “beam” which is the round part near the animal’s head.  This part usually has much more dense material, and I’ve chosen a slice of this to turn my kagamibuta bowl from.

Above is the slice of moose antler I’ve chosen, and I’ve used common wood glue to glue the slice to a sacrificial piece of hardwood.  You can also see the original damaged ivory bowl, the netsuke lid, and another thin slice from the same part of the antler.  I’ll use this slice for experimental trials later when I’m ready to begin coloring the bowl.  Since antler varies from piece to piece, and from area to area even on the same antler, it’s important to use an experimental piece from near the same location.

More of a side view.

Above is the antler and sacrificial hardwood block mounted in my little Sherline metal-cutting lathe, ready to begin turning.  I’ve used a small four jaw chuck here, and worked diligently to get the center of the antler  centered with the lathe axis.

Here I’ve begun turning the irregular antler into a perfect cylinder.  I’m “sneaking” up on the appropriate outside dimension, carefully measuring with calipers several times until I arrive at the 1.75 inch desired diameter.  Hopefully, all of the outside “skin” of the antler will be gone by then.  I’m a great fan of leaving “natural” parts of the antler skin in place, but since this a replacement part for an ivory bowl, it needs to be smooth and unmarked.

Here’s the blank cylinder at the final outside dimension.  By the way, the part where the lid/plate will go is on the exposed end.  I now need to take a “facing” cut across the end to smooth it out and make sure the end is at perfect right angle to the cylinder.  I’ve used a “trick” to help with seeing the cutting in this blandly white material by coloring it with a pencil, making certain I cut away all of the black parts.

And, above, is the finished and pretty smooth face of the cylinder.  Next, I have to drill an axial hole through the whole thing for the cord hole.