Red Copper Oxide Patina

Red Copper by Mrs. Kuroki
Frame by me

So many of my fellow metalsmiths are eager to learn how I achieve the red color on copper which I use a lot in my jewelry. These are definitely some of my most popular pieces of jewelry. Most people are curious what the material is because it doesn't look like what people think of when they think of copper.


I learned this method in Japan about twenty years ago from my teacher, Ayako Kuroki. She called it "houshyayaki" which translates to "grilled borax". Mrs. Kuroki taught me how to achieve a solid red patina which isn't always easy. I didn't have a problem getting the results I wanted at first. But a few years ago I lost my touch for some reason. After many frustrated attempts I finally threw in the towel and decided to take a break from it.

Earrings made in Japan circa 1990
Photographed upside down by man who doesn't wear jewelry!

Due to popular demand from both customers and other jewelers wanting to know how I do it, I started trying it again last night. It looks like there's hope that I may be able to figure it out. The more I practice the better I'll get at it which has always been the case from the first time I learned this technique.

This is all you need.  So simple...yet so not!

It's actually a very simple method. You simply mix some borax with tap water in a ceramic bowl which can take the heat of a torch in close proximity. I was taught that the dilution doesn't matter nor does the temperature of the water. You then heat your copper piece with a torch. I use a propane one. I surround the piece with charcoal blocks to help it heat up. You heat it to a red hot and very quickly quench it in the borax/water solution. It usually takes a few rounds before you achieve the solid red. The first attempt is often too orange for my taste. And there are usually black splotches mixed with the red. I was taught to heat from the back of the piece but honestly I have heated from the front with good results many times.  And if it just isn't working I throw the piece in the pickle and start over.  The pickle will remove the patina very quickly.  Which means the piece has to be cold formed.  No soldering.

As far as prepping the copper goes, Mrs. Kuroki thought that hammering it or at least hardening it yielded better results but I have gotten some of my best color on flat pieces of scrap which had no treatment at all. I also give the metal some "tooth" by rubbing it with scotchbrite.  Sometimes the piece has a beautiful shade of red but it's covered by a film which makes it difficult to really see. The best results have a glassy finish with no film.

Domes on left made last night.  You can see the black splotches I mentioned.
The earrings on the right are about 15 years old demonstrating durability.
I've worn them A LOT and thrown them into pockets with keys, etc.

This ring is pretty beat up and I wouldn't be showing it off except
to demonstrate durability again.  This was an experiment to see if
it was possible to inlay into the copper. It's about 15 years old and
worn a lot as well.  What I learned was that the pointy parts of the
inlay are too vulnerable.  But you can see that the red patina keeps
 on tickin'. I learned this inlay from National Living Treasure,
Mitsuo Masuda.  He invented this method of inlay as a modification
of "nunome zougan".  It is called "chidori ishime zougan" or
"bird's foot inlay".  I'll do another blog posting about Masuda Sensei
and this inlay technique sometime.

I'm no scientist, so I don't understand exactly what is going on in this process. But I believe that the borax is forming a glassy crust on the surface of the piece.  The red color is just a layer of oxidation and there is a core of the pink copper we are used to inside.  It is very durable as you can see in the photos of pieces I made about 20 years ago and have worn and manhandled many times. One would have to take a graver and carve into it to see the pink copper underneath.

I'm sure there are people out there who do understand the science behind it and I would love anybody to chime in with their knowledge/opinions.      

Cool Japanese Tools

Traditional Japanese metal polishing tools

I lived in Japan for six years and was fortunate to be able to study traditional Japanese metalsmithing at the Kuroki Atelier in Daikanyama, Tokyo. It is common knowledge that when the Japanese undertake something, they are not half-assed about it.  I was in total awe of the level of skill and craftsmanship they were capable of in all crafts.  They have so many skills and techniques which are unique to their culture.  When I learned how to polish metal in the old style I fell in love with the tools themselves.  These were being used long before electric power machines such as flex shafts and buffing machine came around.  Take a look...

1. Stage One ~ Naguratoishi

Naguratoishi is a stone.  The first stage of polishing is using this stone by dipping it in water and rubbing the piece of metal in a circular motion thereby eliminating the top layer of scratches.

Naguratoishi

2. Stage Two ~ Hozumi

Hozumi is a soft charcoal.  This stage is just a repetition of the first stage using water to polish the even finer scratches left.

Hozumi

3. Stage Three ~ Dozuribake

And then we have dozuribake which breaks down in translation to copper/polish/brush.  I think this is the coolest, most beautiful tool I've ever seen.  It's made from human hair which runs through the entire piece.  As the hair gets worn down from polishing, you shave off a layer of the enclosing wood frame.

Dozuribake

4. Stage 4 ~ Hozumi powder

The final stage involves grating the hozumi with a coarse file into powder.  You then add a little water to the powder, dip the dozuribake into it and polish using a circular motion for the final stage.

Hozumi Filings

Polishing with Dozuribake

This method of polishing doesn't result in a shiny finish but is more of a sheen I would say.  These earrings and brooch which I made illustrate the kind of finish you get with this method.  The Japanese aesthetic favors the subtle which is expressed in a word which cannot be translated into English: Shibui http://en.wikipedia.org/wiki/Shibui