I have no good opinions on this, but is some input.
If the only justification is that soda lime glass is not involved, that is not convincing because other glasses also have sodium flare.
I have a book, Torch-fired enamel jewelry, in which the author (Barbara Lewis) advises that, "Torch firing enamel does not produce the bright light of lampworking." (p. 1
. That indicates to me that torch firing is intended to melt the glass only and not excite the glass sufficiently to produce light. Perhaps if over-fired, the flare might be present.
A related example is a demonstration of bead surface decoration with stringer that I recently attended: The presenter used a Hot Head to decorate a pre-made base bead and, from what I remember, said that dydimium lenses were not required. Obviously, in this case, a sodium flare will be produced if the glass is held in the flame, but that is not intended with this technique.
Then again, a vendor of glassblowing and flameworking eyewear, if I remember correctly, says that the sodium flare is not the dangerous part of the light emissions while glass working, and is an inconvenience, while the non-visible emissions (UV/IR) are the danger to your eyesight.
Having said that, I ended up on the Phillips Safety website blog, where there was a question about vitreous enameling:
Tim O'Neill
September 23, 2013 | 9:33 pm
I am doing vitreous enameling and would like to know what lens type you would recommend.
Reply
Kieran Hunt
October 10, 2013 | 7:27 pm
Hi Tim,
Great question!
Since you’re working with borosilicate glass in vitreous enameling, in general we recommend our Green Ace Shade 3 lenses. If these are too light for you, you can return them for a Green Ace Shade 5 (as long as you didn’t order them in prescription), but the 3 should work for you.
Please let me know if you’re wondering anything else!
Thanks,
Kieran Hunt
Phillips Safety Products, Inc.