As early as 1941 Klemm and Smekal (1941) wrote in a contribution to this journal that etching of well-polished glass surfaces reveals hidden "polishing scratches" caused by the action of grains in the polishing compound. These authors contended that polishing grains must be harder than the glass that is to be polished, and that polishing is a continuous thermoplastic flattening or smoothing of surface irregularities due to a succession of crisscrossing smooth, very small scratch marks caused by the hard corner points of the polishing grains and with a minimum of material removal. They later expanded their theory of the basic mechanism of polishing (Klemm 1950; Smekal 1950); Smekal added the opinion that any grinding compound can be used also for polishing, provided that its grains are fine enough.
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