Doctor Wood. Modern Wizard of the Laboratory: The Story of an American Small Boy Who Became the Most Daring and Original Experimental Physicist of Our Day-but Never Grew Up

I prepared an alloy of pure gold and a very small fraction of 1 per cent of iron, hammered the bead into the form of a disk, and heated it over a very minute flame. At a temperature a little below a dull red heat a beautiful purple film formed, matching the color of the sequins almost exactly. As I could not ascertain the effect of three thousand years of exposure to the air on one of my alloy plates, I was obliged to look for other evidence that the color was produced by the heat process. I removed the purple film from a small piece of one of the sequins by nitromuriatic acid and examined the gold with the microscope. The surface had been etched by the acid and showed a very marked crystalline structure. A similar treatment of one of my replicas revealed the same crystalline structure, which was not shown by specimens which had not been heated to a high temperature after the hammering process. Pure gold rolled into a thin plate between steel rollers shows only very minute crystals when etched, but if heated shows crystals of exactly the same size and character as those found in the Egyptian sequins. This was proof number one that the sequins had been heated after their manufacture.

Proof number two came as a result of an investigation of another surface characteristic of the sequins, the invariable, presence of minute metal globules of gold which stood up in high relief on both sides of the sequins. Obviously these must have been formed after the ornaments had been hammered or rolled into shape, and one or two had the form of minute mushroom buds, a globule supported on a short stem. This suggested that they had been exuded or excreted by the metal, by a process similar to that which occurs when a silver bead is heated on charcoal by the blowpipe flame, the phenomenon referred to as the “spitting of silver”. It results from the liberation of dissolved gas at the moment of solidification of the globule. I was unable to find any allusion to a similar performance by gold and for some time was unable to produce the globules on my replicas.

The solution of the problem came in a rather fantastic way. I had made spark spectra of the purple sequins and found practically no lines save those of gold and iron, the latter being quite strong. A more careful scrutiny revealed a few very faint lines which could not be attributed to either metal, and two of these I attributed to arsenic. I next heated a small fragment of one of the sequins in a small tube of fused quartz to a temperature considerably above the melting-point of the gold in a very slow stream of hydrogen, and found a deposit on the wall of the tube beyond the heated portion, a yellow and a black ring, the latter on the side away from the gold. I therefore suspected the presence of sulphur and arsenic, and native sulphide of arsenic (the yellow pigment orpiment) was in fact imported into Egypt during the Eighteenth Dynasty and used in tomb decorations. This suggested that the royal goldsmith had perhaps tried the experiment of fusing gold with the yellow pigment in the hope of improving the color or of getting more gold. I wrote to Mr. Lucas asking for a few minute scrapings of this material, and he sent me some small lumps that had been found in a cloth bag in the tomb of Tutankhamen. I fused a small speck of this substance wrapped up in a pellet of thin gold plate, and as the fused globule solidified it “spit” out a small globule exactly as silver does. But a thin plate hammered from this globule and then heated showed no trace of further “spitting”.

It was now obvious that the gold and orpiment would have to be melted together and solidified under pressure to obtain a specimen that would “spit” after being fashioned into a plate by hammering or rolling. I accordingly heated the two in a small sealed tube of fused quartz, melting the gold down to a round globule. Some of the sulphur and arsenic was liberated as vapor under pressure and glowed bright red in the non- luminous tube (for quartz radiates practically no light even at very high temperatures). After cooling, the tube was opened and a plate hammered and rolled from the globule. When heated to a dull red heat the plate grew a marvelous crop of metal mushrooms.

This suggested that the necessary pressure required for keeping sufficient arsenic and sulphur in the gold to produce “spitting” may have resulted from the fusion of a considerable mass in a crucible, for we know from the bas-reliefs at Saqqara that the Egyptians used furnaces operated by air blasts from human lungs. But there was another and more probable alternative, namely, that the sequins had been fashioned from native gold nuggets which contained a trace of iron as an impurity. These, having been originally formed deep in the earth and under pressure, might easily contain sulphides, arsenates, or similar gas-producing compounds in sufficient quantity to produce the small amount of “spitting” shown by the sequins.