Hi: I am looking at the "Covington buff & polish chart" and it references A, B, C, and D. I do not find a reference as to what those materials are. Also, when is Alumnia A used?

When looking at the chart its best to match the letters across the rows for the best combination. For example on agate it shows an A for felt and an A for cerium which means a Felt buff/pad would work best with cerium for agates. The second best option would be Leather and cerium followed by the third best option, phenolic and diamond.