Hmty Km, the original black copper alloy

2017-05-02 14.51.03In working on our MMA reconstruction piece, I’ve been researching ancient bronze to better understand the composition of the tools we will be making. There is very little information out there on Etruscan era tools, and according to other who have studied this the tools were either melted down or corroded beyond recognition. I contacted two experts in ancient metallurgy from (a treasure trove of free information that I turn to often) and Dr Alessandra R G Giumlia-Mair has some helpful analysis she is willing to share. I find scientists to be incredibly helpful and willing to share information. It’s a great example to emulate in projects like this.

In reading some of her research papers, I came across the topic of Hmty Km (pronounced “hempty kem”) an Egyptian black copper alloy that is the predecessor of Shakudo in Japan, wu tong in China and was called Corinthian copper in the West. Apparently its use died out in the western world after it traveled to asia. This is the reason it is considered a Japanese technique today, its Egyptian and western beginnings being largely forgotten. It is primarily copper with small amounts of precious metals like gold and/or silver. Even percentages as small as 1 or 2 % gold greatly alter the patinas you can achieve. Of course, I was intrigued and had to whip some up right away. There are many, many recipes to choose from so I started with a few straightforward ones. An important element in many of the original alloys  is arsenical copper, or copper ore with arsenic in it, as it occurs in nature. Yikes! From my research so far, it seems the arsenic makes a harder alloy. Unless or until I can figure out a way to use the arsenic safely (which is doubtful) I will make do with a softer arsenic-free alloy. It remains unclear to me what effect, if any, the arsenic has on the patina of the finished piece but I might not be able to test that for safety reasons. It’s all fun and games in the studio until you give yourself arsenic poisoning….

The recipes I made are 94% Copper 6% Gold, 93% Copper 6% Gold 1% Silver and 70% Copper and 30% gold. We will see how they turn out when patinated but the shades are very lovely as is. Of course, if I wanted to keep them this shade they would have to be waxed or lacquered to seal in the color and keep them from oxidizing.6% Au 94% Cu alloy

left 6% right 30% AuLeft 94% Copper 6% gold, right 70% Copper 30% gold