Sciencemadness Discussion Board

UV Light and Blocking

CHRIS25 - 2-9-2012 at 03:12

Direct questions into google turn up nothing, physics sites force you through pages of of data without knowing whether or not you will get the answer. It's a simple question that I can not find a simple direct answer to on the internet and would be grateful for the answer please.

What colours block UV light, the few tit bits that I have found suggest yellow and brown, yellow and amber. But this was a casual comment. I need to use pigment inks to block UV, Black I know works, but I need to increase the block a bit with yellow or red? Or a mixture of both. (This has to do with Potassium Ferrocyanide and ferric aluminium citrate). So some final concrete answer would be so appreciated. Thankyou.

kristofvagyok - 2-9-2012 at 03:47

In a photo lab we use red lights and red filters if the BW photopaper(extremely sensitive to UV) is taken out from the casing.

If the red filter is attachet to the photoenlarger, then the photopaper could be placed under it and could be modified a bit, while it won't get damaged, but if any else light source will reach the paper it will get darkened in a minute.

So: use red.

Or if glass is needed, then use brown reagent bottle, they also block UV in high percent, but the absolutely best is the brown bottle coated with a black polymer film.

But as I remember this question was discussed a few month ago....

[Edited on 2-9-2012 by kristofvagyok]

bquirky - 2-9-2012 at 08:29

the simple answer is definitely red..

Red things appear red because they absorb blue light. since UV is closesr to blue it will generally be absorbed more by red objects and reflected by blue.

Blue/UV light has more energy per photon and This is indecently the reason why red things fade the most when outdoors.

look at any old shop sign that has red in it or plastic objects that get left outside like kids play toys the red always fades worst

Transparent glass or plastic blocks alot of UV but definitely not all. if you where trying to keep it out id suggest black paper/plastic or non crinkled AL foil

CHRIS25 - 2-9-2012 at 13:25

Hi Guys, I think I should havebeen more plain, I am not refrring to putting things in storage. I am actually referring to pigment ink. I mentioned it above but not clearly enough, I want to block UV light with inkjet pigment ink, not resin ink. Black does a lot of blocking but not enough, I have heard that yellow is the next best thing, but red and yellow mixed in equal parts is also a possibility. I was therefore looking for some science on this rather than photographers' opinions.

platedish29 - 2-9-2012 at 22:10

I didn't know paints could work in the invisible spectrum like that! Interesting information you provided. Why dont you try useing a UV lamp crossed by paint and highlighter fluid in the other side?

bquirky - 2-9-2012 at 23:29

Can you use a laser printer ? people use toner for UV masking all the time making PCB Bords

perhaps you can print on the same peice of paper multiple times to get a higher pigment loading

CHRIS25 - 3-9-2012 at 02:33

Hi Folks. Well firstly I can not get hold of a suitable UV set up, I am no good at electrics and so can not build one. I use the sun, it's free and not complicated to set up. Facial lamps are ideal and reasonably priced but hard to get in Ireland, the lamps I have to order from England, so you can see it's all a pain. Hence asking. I am printing on Transparency to get a negative, many tests have shown how matte black pigment ink works fine (don't use gloss as recommended) but black by itself does not work in shadow areas where less ink is laid down for the UV to penetrate. I add yellow to the black ink and this helps a bit. But I thought I would ask the question because Red also works - trouble is I did not want to be wasting valuable ink, so thought someone might have a definitive answer, such as black yellow red, or black red+yellow in equal amounts, just to save me bit of time and a lot of ink and transparency paper. bquirky, I don't have a laser printer, but this would not be good enough for the photograph.

[Edited on 3-9-2012 by CHRIS25]

watson.fawkes - 3-9-2012 at 07:23

Quote: Originally posted by CHRIS25  
But I thought I would ask the question because Red also works - trouble is I did not want to be wasting valuable ink, so thought someone might have a definitive answer, such as black yellow red, or black red+yellow in equal amounts, just to save me bit of time and a lot of ink and transparency paper.
Frankly, without knowing the composition of the proprietary pigments and their dye spectra, it's hard to say for sure whether one color will generically work at a different band.

Instead, I suggest that you make up a test page in Adobe Illustrator or somesuch, print a test page, and minimize the amount of ink you spend on validating what you end up using. This is likely going to get you a good result faster than fiddling with parameters on single images. Since it's gray scales that are the problem, you want gradient fills. You want one large bar for each pigment color; I assume that's four. Then you want a bi-gradient square for each pair of pigments. That would be six. And then you want to be able to specify in the output stage that certain colors correspond exactly to different pigments, which I am given to understand Illustrator supports for things like Pantone pigments, although I have no idea of the details. Make sure to put witness marks, graticules, and numbers on the axes. After you've got the test page, expose it. You should be able to determine what's acceptable by examination of the result. And if you're reusing a mask, you could leave a test page in the sun for a while to see if/when you might have a problem with UV degradation.

(edit) Postscript : I seem to recall that some folks have developed UV-resist pigment inks for circuit board work. They're sold as DIY refills, as I recall. Now I understand your reluctance for mail order, but it's entirely possible that you'll get an overall-cheaper process by using a purpose-made pigment rather than pressing into service one that's not designed for it.

[Edited on 3-9-2012 by watson.fawkes]

CHRIS25 - 3-9-2012 at 09:39

Funny Watson, I never thought about doing what you said. I have nine inks on my printer - that's a lot of combinations, but I know that I can eliminate cyan and light cyan. So I will use yellow, magenta, light magenta the three blacks I think. The made for UV blokkers I am aware of, unfortunatley that woul dmean re-designing the ink flow in a printer which of course would be a volcanic disaster. But your testing plan seems very practical, why didn't I think of that?

[Edited on 3-9-2012 by CHRIS25]

watson.fawkes - 3-9-2012 at 18:14

Quote: Originally posted by CHRIS25  
Funny Watson, I never thought about doing what you said. I have nine inks on my printer - that's a lot of combinations, but I know that I can eliminate cyan and light cyan. [...] But your testing plan seems very practical, why didn't I think of that?
I'd test even your cyan and light cyan, at least with single gradient bars. Not that I'd hold high hopes, but you might get lucky that they happen to be UV-opaque. Perhaps with nine inks you might simply start with just gradient bars and do bi-gradient squares on a second pass with the most promising candidates.

As for why you didn't think of, it's likely because the concept of a "parameter space" is ordinary to scientists and moreso to mathematicians. A parameter space is the conceptual space of all possible combinations of the variable parameters in a given situation. In the case of your printer, it's a 9-dimensional cube, that is, nine numbers each ranging from zero (no ink) to one (max ink). My idea is really to sample with parameter space with some test patterns.

platedish29 - 3-9-2012 at 18:56

You mean, many empirical x-Y% combinatory?

CHRIS25 - 5-9-2012 at 06:41

OK, well, I decided not to waste expensive ink and valuable time by experimenting with all inks. I decided to concentrate on certainties and leave futility behind. After studying a wee bit about the colour spectrum, I chose to take the Matte black which is a known UV blocker, albeit not 100%, and it's the "not 100%' that is bothering me, so with matte black I added a combination of yellow and magenta, now exactly how much this is in picolitres I will never ever know, but the arbitrary measurements are all that I need. It worked pretty well so far, but I need to do more testing. Yellow and magenta are directly opposite Cyan, and since cyan is green and blue this makes sense as to these colours being very weak UV blockers. Yellow and magenta make red, and red is opposite the cyan. So everything is going well. Just in case anyone is confused - I'm sorry - I am referring to the RGB spectrum and CMYK physical ink. Not the colours that painters mix. Adding yellow and magenta to black I think gives brown, but I am no expert on colours, and I guess it's not the brown that is important, more that yellow and magenta are high UV blockers on the colour spectrum. So glad I didn't need maths for all this......

ItsAChitzen - 10-9-2012 at 11:05

How far into the UV do you need to go?