U of S | Mailing List Archive | alt-photo-process-l | Re: green-yellow

Re: green-yellow

Thank you for finally chiming in on this issue, when Loris asked the original question of why does cyan and yellow together hold back more light than one would presuppose from the way they individually hold back light? Your answer raises some interesting points.

I have posted my bw paper example here for what it is worth (apparently nothing to certain listees) for an illustration of color under tungsten not UV light:

Now, let me get this straight:

1. Alberto said: (cut)
Perhaps one response might have been: because adding another UV blocker to that contained in the yellow ink increases the total opacity towards UV.
UV absorption of an organic molecule relies mostly to the presence of double bonds. How many they are -and their UV absorption- is almost independent on the visible color: you can have a perfecly transparent substance in the visible range which is UV opaque. A factor 30 sun oil is not black, only perhaps very faint yellow...
I don't know what molecules are in the inks the different printers and their different models use, but considering also the additives that certainly are in the inks, there are many reasons for believing they all are different enough.
This is a PERFECT example to tell my students! If you remember, the original intent of my circles was to show students that the relative lightness/darkness of a color does not predict how well it holds back UV light. But now I will couple that with the sunblock example!! Excited. So your answer/conjecture (?fact?) to Loris' question is the presence of more double bonds in the colors mixed or in the stuff the ink is suspended in. I suppose it'd be a cold day in hell before Epson would tell us any of this proprietary info. Not that I care in the long run as practice is what is important.

2. Alberto said:
> What I was trying to say in my previous post was that it is a nonsense to
infer a UV absorption from the visible color of a pigmented matter, whatever it is. All the arguments about complementary colors (yellow/blue, red/magenta, etc) hold only in the visible range.
It is nonsense, but not to Twentysomethings :) But apparently Loris, myself, and others find yellow in the Ultrachrome inks to be the densest, whatever the reason if not its color (on 6 different printers for me, but all Epson) but that is not a quantative fact, because it does not related necessarily to dye based printers or HP printers...but it seems I should be careful to "couple" its UV blocking nature to its color opposite the UV spectrum as I think you are saying. I will stand corrected.

Now, a question for Loris and then back to Alberto:

3. Loris, you said that you "know" that printers do not lay down more ink when mixing a color. Is that a for sure fact or a surmise? Because let's just deal with the visible light example in my BW print then. If you see, the combination of yellow and magenta to produce red holds back the most light, but if you look at the yellow alone and the magenta alone it is hard to make that "leap" from those darknesses to the combination of the two colors, which holds back more light than even black. Which, at least for me, provides more food for thought about the printer drivers. But if you KNOW that is a fact then I will remove that conjecture from my mind.

4. Alberto, did you at all get affected by the earthquake? It has been on the news lots here and I offer condolences. It makes the puny blow up downtown Bozeman pale in comparison. I hope you were nowhere near/had no relatives affected :(