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

Re: green-yellow

When I asked a question on another forum about this a couple of years ago, I was told that the farther the color is from violet on the spectrum, the better it will block UV. By this logic, the UV- blocking capability of colors should be in descending order: red, yellow, green, cyan, blue, magenta. This makes sense theoretically, but in practice it doesn't always seem to come out that way, in fact the ranking of colors by blocking ability seems variable depending more on the printer, the inkset and the light source than on the process.
In other -and less- words, it depends on the UV adsorption of the inks and not from the absorption in the visible range. Many animals different from humans behave in this way. We need to think not from what we see (visible spectrum) but from what we don't see (UV range). This is not possible unless, like Marek suggested, we perform a strumental reading.
After printing my colour tests, sometimes it happens that the black outlier is "less white" than the coloured squares. My answer is that the black inks/pigments have window in the UV range, which I (an human) can't see.
I only do the one process, so can't compare profiles across processes, but I've seen several examples where people have used the HSL array for different processes, using the same light source, and got exactly the same HSL profile for the different processes, which suggests to me that it's the printer inks and the light source that determine the color blocking profile, not the process.
I work with many processes but with my printer (Epson R2400) and my light source, I have negatives with different hues, chiefly in shades of green and red (also towards orange) depending on the process though printer, light source and transparent medium are the same. This is a little frustrating because I know in advance that every time I begin a new proces, I need to calibrate everything like it were the first time I do it.