VIII.—Quarries. (Size of originals, 4-1/2 by 4 ins.)
PLATE IX.—Micro-photographs. 1. A piece of outline that has "fried" in the kiln. Magnified 20 diameters. See p. 104.
2. A small Diamond seen from above. Magnified 10-1/2 diameters. The white horizontal line is the cutting edge.
3. A larger Diamond that has been "reset."
That is to say, re-ground: the diagonal marks like a St. Andrew's Cross show the grinding down of the old facets by which the new cutting edge has been produced. Magnified 10-1/2 diameters.
4. No. 2 seen from the side. Magnified 10-1/2 diameters; the cutting edge faces towards the left.
IX.—Micro-photographs from details connected with Glass Work.
PLATE X.—Micro-photographs of Glass-cutting Very difficult to explain. "A" is a sheet of glass seen in section multiplied 15-1/2 diameters. The black marks along the top edge are diamond-cuts, good and bad, coming straight towards the spectator. The two outside ones are very bad cuts, far too violent, and have split off the surface of the glass. Of the two inner ones the left-hand one is an ideally good cut, no disturbance of the surface having occurred; the right-hand a fairly good one, but a little unnecessarily hard. Passing over B for the present—C is a similar piece of glass also magnified 15-1/2 diameters, with wheel-cuts seen endwise (coming towards the spectator). The one on the left is a very bad cut, the surface of the glass having actually split off in flakes, the next to it is a perfect cut where the surface is intact, and note that though not a quarter
so much pressure has been employed, the split downward into the glass is deeper and sharper than in the violent cut to the left, as is also the case with the two other moderately good cuts to the right.