The trick is the ampoule itself. If I used a brand new, clean pyrex tube and clean it with Alconox, the molten metal seems to find faint residues on
the glass that were invisible. If I clean the tubes with conc. H2SO4 @ 200-300 C for 5 min, this glass has far fewer film formers found on it. It,
however, seems to be much less "slippery" to errant beads of metal which makes a totally clean seal (no darkening of the glass) very hard to achieve.
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