Drilling Fluids Materials (includes Addendum 1 dated April 2020 and Addendum 2 dated June 2022) Covers physical properties and test pr ocedures for materials manufactured for use in oil - and gas - well drilling fluids. The materials covered are barite; hematite; bentonite; non - treated bentonit e; attapulgite; sepiolite; technical grade, low - viscosity carboxymethyl cellulose (CMC - LVT); technical grade, high - viscosity carboxymethyl cellulose (CMC - HVT); starch; low - viscosity polyanionic cellulose (PAC - LV); high - viscosity poly anionic cellulose (PAC - HV); and drilling - grade xanthan gum. This specification is intended for the use of manufacturers, distributors, and end users of named products. Annex A (informative) contains information on the API Monogram Program and requirements for the approved use of the API Monogram by licensees