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Nak 12-12-11 12:30 PM

Barium Sulphate
 

Has anyone tried mixing Barium Sulphate with a screen paint? It looks like it would reduce the amount of light absorbed by the paint and increase the amount reflected. http://www.usu.edu/cpl/PDF/Barium_Sulfate.pdf
It might only work for a white paint, but perhaps it would help a gray paint as well. I wouldn't think it would help any paint with reflective particles within it though.

Harpmaker 12-12-11 08:52 PM

Re: Barium Sulphate
 

Quote:

Nak wrote: (Post 480426)
Has anyone tried mixing Barium Sulphate with a screen paint? It looks like it would reduce the amount of light absorbed by the paint and increase the amount reflected. http://www.usu.edu/cpl/PDF/Barium_Sulfate.pdf
It might only work for a white paint, but perhaps it would help a gray paint as well. I wouldn't think it would help any paint with reflective particles within it though.

Thanks for the link! I had seen that info before, but forgotten about it.

To put that article in context they were talking about using white paint and barium sulfate to create what we commonly call a Unity target used in gain testing (or any other testing that requires a target as close to a perfect lambertian diffusive surface as possible). The problem with using pure barium sulfate powder is that it must be compressed into a flat disk of the desired size. Such a disk is very fragile and is easy to break. Instead of using a compressed disk many choose to use a plastic target (Teflon or Spectalon) which exhibits similar optical properties, but are much more durable.

I see no reason why a paint such as mentioned in the article couldn't be used as a screen paint, but testing would have to be done to make sure the barium sulfate did not react chemically with the paint used and change color. For example, Mech and I use blocks of magnesium carbonate (gym chalk) as Unity targets. I figured I might as well try crushing some to a powder and adding it to a clear medium (I think it was Valspar Clear Protector), but when I did that the nice white powder turned almost as yellow as a lemon!

Another factor is cost. I found barium sulfate for about $23 for 500 g. with shipping. The best mix according to the article is a 50/50 mix by weight. 500 g. converts to around 17.6 ounces. I'm not sure how much white paint weighs, but I suspect it wouldn't take very many fluid ounces to equal 17.6 ounces by weight. That would make the paint quite expensive and you are only gaining at most 4% more brightness over regular titanium dioxide white paint; but if you really needed those 4% this might be the way to do it!

BTW, in case you noticed that in the first chart the pure barium sulfate gave a reflectance over 100% from about 580nm to 460nm (greenish-yellow to dark blue) the only way that can happen is for the target to be fluorescing (converting ultraviolet light into visible light).

There would be no sense to use barium sulfate in gray paint since it would only take more tint to create the desired shade of gray.

Nak 12-14-11 10:10 PM

Re: Barium Sulphate
 

Thanks Harp!

I weighed a gallon of paint, around 7 pounds. So if you were to paint a screen with half a gallon of paint, you'd need just under 2 pounds of and just under 2 pounds of paint. You'd need to buy 1000 grams of the ... Interesting initials. :D

I re-read the article, 100% is normalized to the Spectralon reflectance. So by sowig over 100% it's just saying it reflects better than the Spectralon. Of course, since I'm not sure what the Spectralon curve looks like, it's hard to say what the curve of this mix really is.

Harpmaker 12-14-11 11:44 PM

Re: Barium Sulphate
 

Spectralon's reflectance curve is quite flat in the visible light spectrum, but IIRC the stuff is EXPENSIVE. Just checked and the cheapest target I could find is $346.

For more info on Spectralon than you care to know check out this PDF (reflectance data on page 10):
http://www.pro-lite.co.uk/File/Tech_..._Materials.pdf

There is actually a set of white and gray Spectralon targets available. See this PDF (some of the grays don't look that flat).
http://www.pro-lite.co.uk/File/LAB%2...ct%20Sheet.pdf

Alvinsummer 08-15-18 02:32 AM

Re: Barium Sulphate
 

As a factory who produce the barium sulfate. i can tell you the barium sulfate can be used in white paint. If other color paint need to use other pigment. www.sinokematerial.com


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