Linde B is a graded calcined gamma-alumina polishing compound with a nominal particle size of approximately 0.05 micrometres, finer than Linde A despite its later letter designation. The naming convention reflects the original Linde Air Products specification system, in which letter codes corresponded to particle size ranges rather than to alphabetical ordering. Linde B is widely used in metallographic sample preparation and as a final polishing compound for some gem species; in lapidary practice it is sometimes substituted for Linde A on the softest gem materials where minimal aggressive cutting is required.

Composition

Linde B is gamma-alumina, a different crystalline phase from the alpha-alumina of Linde A, with a lower hardness and gentler polishing action. The particle size is more tightly graded than Linde A and the median diameter is smaller, producing a higher-quality final polish on materials too soft to tolerate Linde A without surface deformation. Both Linde A and Linde B have been continuously available in laboratory-supply channels under various manufacturer labels since the original Linde Air Products production runs of the mid-twentieth century.

Lapidary use

In gem cutting Linde B is sometimes used as the final polishing compound for very soft species (fluorite, calcite, certain phosphates) where Linde A causes microscopic surface plucking or undercut polishing. It is generally applied on a tin or zinc lap with water as the carrier. For most facetted-corundum and harder coloured-stone work, Linde A remains the standard; Linde B is a specialist's choice for marginal cases.