Quote Originally Posted by Ken Nadvornick View Post
From the generated line spectrum of an LPS lamp the extra blues and greens caused by the inclusion of the argon/neon Penning mixture are readily apparent. And a look at the #19 Fire filter chart shows that it should be almost perfectly opaque to those wavelengths all by itself. For standard OC-rated b&w materials this filter should work fine. And in practice, at least for me, it does.

On the other hand, I'm not sure what additional safeness the other two filters would add, given their respective charts. Especially in the green regions for VC papers. Filter #3407 in particular allows a substantial percentage of blue-greens and greens to pass. This should be an obvious risk factor for VC papers if the #19 were not present.
This is the part that confuses me. The 19 filter is only supposed to allow the passage of a slight percentage of green-ish wavelengths, and this was very evident in my not-at-all scientific test; there was a definite green band right where one would expect it, were they looking at the chart for the 19 filter. I was under the impression that this wouldn't be an issue when I ordered the 19 and 27 filters, because I'd read so many reports of them being great cutoff filters for the sodium lamp...but somehow I still got a definite graying of the paper after less than a minute's time. With that said, I can't figure out how the other two filter numbers would help, because they seem to be letting in a lot of blue/green wavelengths.

Quote Originally Posted by frobozz View Post
Well, we need a cross-reference between Thomas' "edge tape color" based ID scheme, and the various gel colors, but as a clue, here are the official instructions from Thomas (I scanned the sheets that came with mine):
I just found that online not too long ago; thanks for posting it!

Quote Originally Posted by Greg Davis View Post
I purchased a set from Freestyle while Thomas was still in business. I bought a yellow tape, a red tape, and a black tape. I took them apart a few years later to see if they were filters I could replace myself for less money. In the yellow tape filter I found two sheets of gel filter material. One had the number 3407, the other 3406. I recognized them as Rosco filters from my sample book. The red tape had "ROSCO 19" printed on the edge of the filter. The black tape did not have any markings, but were the same colors as the yellow tape, but used more layers of filter material inside. All of them used the tissue paper that comes with Rosco filters as the diffusion material.

The numbers were not present in both filters of a pair. I don't think they were intended to be left on the filter material when cut and put in place. I had a very old set of Thomas Duplex filters, and they were different material. It was far too old and faded to tell what they once were. It is possible that the filters sold for these safelights now and just before Thomas Duplex stopped selling their lights are made by someone else and they just use what they think may work, but if you buy a set of filters from Freestyle or KHB Photographix, these are what you get.

You could always buy a set, open them, and tell us what is in them. If they are different than what I have, then I was sold the wrong filters. But I doubt it.
I think the filters I had in mine when I got it were the older style, as well...and they were desiccated beyond recognition. I'm almost tempted to buy the inner set and see what comes in them...but that may have to wait until I have some extra cash. For now, I'm hoping that the rubylith I ordered will come in soon and hopefully allow me to actually use the safelight, rather than just look at it.