For measuring the brightness of some materials, some dated industrial methods cite a Magnesium Carbonate block standard to be set to Y = 100% in reflectance. This is a very old top-of-scale standard and HunterLab does not recommend using it.
Instead users should update their methods to the current industry standard of a PRD Perfect Reflecting Diffuser as 100% top-of-scale for reflectance. A Magnesium Carbonate plaque will read slightly lower than a PRD standard, typically around 97%.
If you are determined to use a Magnesium Carbonate top-of-scale, a source for Magnesium Carbonate powder that can be pressed into a plaque can be found at:
Magnesium Carbonate, Pentahydrate, white powder
(Magnesite, Carbonic Acid Magnesium Salt)
Pittsburgh, PA USA
Product # S25399
Mr. Philips has spent the last 30 years in product development and management, technical sales, marketing, and business development in several industries. Today, he is the global market development manager for HunterLab, focused on understanding customer needs, providing appropriate solutions and education, and helping to solve customer color challenges across these industries and cultures.