What was the unknown catalyst which allowed Proto-Adamantium to exist?

We keep looking for an unknown agent but we must look at the fact:

Dr. Myron MacLain used an experimental Steel alloy and Vibranium; He did numerous test using different setting and combination (amount of components, different pressures and temperatures) all of them were obviously recorded. During one of those tests he fall asleep while waiting for the metal to "heat up".

So what was responsible for the Proto-Adamantium formation since we know all the main component of the shield?