I have examined the glass to metal seals and evacuation tubes of various light bulb. I have also worked the glass in a reducing flame but neither my
working or the manufacturer has left the metallic gray black discoloration typical of leaded soda glass.
I suspected the glass does not contain significant amounts of lead. So I checked. Apparently the Europe Union banned leaded glass in light bulbs in
2011. See Attachment: leaded-glass-S1878029612006184.htm (80kB) This file has been downloaded 325 times
That's good news if you are in Europe and you want to work old fluorescent tubes with the cheap torches that have reducing flames. The bad news is
the higher softening temperature requires a hotter flame.
On a different point from that paper "Leaded fluorescent lamp glass can also be divided into three types according to PbO concentration as
light red lead, medium red lead, heavy red lead, which is 11%, 20%, and above 28% PbO respectively" No wounder it goes black in a reducing flame.
Clear_horizons_glass - 13-10-2020 at 10:45
So in your experience lead glass require a much more oxidizing flame to not develop the dark discoloration? wg48temp9 - 13-10-2020 at 14:04
So in your experience lead glass require a much more oxidizing flame to not develop the dark discoloration?
My experience is that a reducing flame reduces the lead in glass to lead metal. I would assume a neutral or an oxidising flame would not reduce the
lead to metal. I can not confirm that by my direct experience because I have never worked glass containing lead with a neutral or oxidising flame.
Though I have read that that is the case.
