THE SHADE OF J. BALLANTINE HANNAY 237
certain depth. To that extent, such diamonds turn blue. Dr. Custers brought one out to show me.
"You will observe," he said, handing it over, "that the coloration is only a surface phenomenon. Hold it sideways and look."
I obeyed him and saw that the stone, except for a thin layer of brilliant blue on one side, was indeed clear and colorless.
"The
coloration never goes more than one fiftieth of an inch deep with this
method," he said, "because the bombarding electrons lose their energy
and are absorbed and scattered if they get in any further. No one has
yet discovered how to make this treatment any more effective:
therefore, looking at it with an eye to commercial uses, I see little
prospect of applying such a process to the manufacture of artificial
fancy stones for the market. Any colored diamond bought for gem
purposes is likely to be one that was found in a mine with that color,
unless it has been temporarily doctored. Moreover, the blue of that
thin layer is not the same kind of color as that of a natural blue
diamond. Let us compare them."
He
brought out a blue diamond that had been cut and polished in the
ordinary brilliant pattern. We set them side by side. He was right; the
natural blue stone had the soft color of sapphire, whereas the other
was greenish blue.
"I
have theories about these natural blue stones, arising from what I have
observed," said Dr. Custers. "Their color may not be due to the
presence of foreign elements. I find it significant that every natural
blue stone we have examined in this laboratory proves to belong to
Type 2-B."
I
asked Dr. Custers just what was meant by 2-A and 2-B, and he
elucidated. For years, researchers in his field have known that
diamonds fall into the two main categories that they call
