Do you have a source for Magnesium Carbonate powder as top-of-scale? Follow

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)
4Mg(CO3)•Mg(OH)2•5H2O

Fisher Scientific
Pittsburgh, PA USA
http://www.fishersci.com
Product # S25399