Cannonball Mold Makes a Dandy Integrating Sphere for Laser Measurements

It's an age-old riddle: if you have a perfect sphere with a perfectly reflective inner surface, will light bounce around inside it forever? The answer is pretty obvious when you think it through, but that doesn't mean that you can't put the principle to use, as we see with this homemade Ulbricht sphere for optical measurements.

If you've never heard of an Ulbricht sphere, don't worry -- it's also known as an integrating sphere, and that makes its function a little more apparent. As [Les Wright] explains, an integrating sphere is an optical element with a hollow spherical cavity that's coated with a diffusely reflective coating. There are two ports in the sphere, one for admitting light -- usually from a laser -- and one for light to exit. The light bounces around inside the sphere and becomes perfectly diffuse, and creates a uniform beam at the exit port.

[Les]' need for an integrating sphere comes from the desire to measure the output of some of his lasers with his Raspberry Pi-based PySpectrometer. Rather than shell out for an expensive commercial integrating sphere, or turn one on a lathe, [Les] turned to an unlikely source: cannonball molds. The inside of the mold was painted with an equally unlikely ultra-white paint concocted from barium sulfate and PVA glue. With a few ports machined into the mold, it works perfectly to diffuse the light from his dye lasers for proper measurements.

Lasers can be an expensive hobby, but [Les] always seems to find a way to make things more affordable and just as good. Whether it's homemade doorknob caps for high-voltage power supplies or blasting the Bayer filter off a cheap CCD camera, he always seems to find a way.

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Scientist Unveil ‘Whitest Paint Ever’ That’s Based on Baryta Photo Paper

Researchers at Purdue University have unveiled what is being called the whitest paint on record, which can reflect up to 98% of light. The paint uses the same chemical compound found in a type of photo paper that has been used by photographers for over a century.

The paint was developed as a way to reduce power consumption for cooling large buildings in the summer as its 98% reflectivity is considerably higher than the 80-90% of light reflected by commonly available white paint on the market. It's even able to reflect infra-red heat, which makes it particularly suitable for this purpose. As reported by The Art Newspaper, it has already shown to reduce surface temperatures of buildings by 4.5 degrees Celcius (8.1 degrees Fahrenheit) below the ambient temperature.

Lead researcher Xiulin Ruan says that they were able to achieve this level of reflectivity due to a high concentration of a chemical compound called barium sulfate, which is used in some photo paper and cosmetics applications.

Barium sulfate photo paper is often referred to as baryta paper. As noted by WhiteWall, Baryta paper has been used by photography professionals for over 140 years.

"Traditional photo papers are made of a coated polyethylene, which makes processing them easier and quicker," WhiteWall writes. "The key difference of baryta paper lies in the barium sulfate (the so-called “baryta”) coating. Ultra-white with a neutral image color, the paper is outstanding at combining brilliant white with intense black tones."

Ruan has already been in contact with an art museum that wishes to display this new white paint next to the blackest material that has been created: VantaBlack. But unlike VantaBlack, which has been essentially privatized and copyrighted by the original creator, Ruan hopes to make this extremely white paint available to consumers and is working with a producer to distribute it within the next one to two years.

If barium sulfate paper is effective in producing better photos due to increasing the perceived levels of contrast, it stands to reason that using this ultra-white paint during the capture process, such as on a cyclorama wall, would also be beneficial. Given that the paint will be available to purchase soon, it will be interesting to see if studios or independent photographers can make use of the highly reflective paint in creative ways, just as has been the case with VantaBlack.

Image credits: Header photo courtesy of Purdue University.

#news #bariumsulfate #barytaphotopaper #photopaper #purdue #purdueuniversity #vantablack #whitepaint #whitestever