Sat 16-Feb-13 11:35 PM | edited Sat 16-Feb-13 11:36 PM by km6xz
Hello JohnE The AA filters used in are made of Lithium Niobate (LiNbO3) which was rated at 5.0Mohs hardness which corresponds to around Vickers microhardness value of 400kg/mm^2 in older materials handbooks but later studies place the microhardness up around 650 kg/mm^2 with the property of increased hardness with increased load. By doping with Fe, which is done to alter the diffraction index (needed in AA filters), increases Vickers microhardness up to around 750kg/mm^2 Here is a study by K G SUBHADRA, K KISHAN RAO and D B SIRDESHMUKH published by Indian Academy of Sciences in 2000 http://www.ias.ac.in/matersci/bmsapr2000/147.pdf that describes the newer findings.
The material is rather inert so is unaffected by any common solvents or water making cleaning safe with just about any solvent you can get without a license. For surface hardness, the newer figures place it close to Quartz crystal, above fused Quartz, above window glass(Moh 5.5), steel and tooth enamel. Stan St Petersburg Russia