For years, there was no direct evidence of the production of glass. Somebody was making it, but the only thing we had were museums full of glass objects.
The mainstream opinion was that the Egyptians were importing it from Mesopotamia. In Egypt, we had only evidence that they were making it into artistic objects.
There were lots of bronze castings, but among all the debris we found a number of things that didn't fit, ... It took me a year or two to figure out that the unusual finds were related to glass.