I have had a little time to experiment with the indirect method of glass engraving and the results are now starting to justify the experimentation time. The glass tiles are 115 x 90 x 4mm in size with polished edges. I am buying them at a wholesale cost of 50 pence per tile. I made an MDF jig for the tiles to fit into so that each tile would automatically be centred after the previous tile was engraved.
My settings for my J-Tech 4.2 Watt diode laser were 95% power and 250mm/min traversal speed. This gives enough time for the laser to create the micro-fractures on the underside of the glass. I used a piece of black card under the glass and a piece of thin aluminium under the card so that in the event of the beam burning through, the jig would not be burnt. The images represent two different approaches to artwork.
The dog (which is slightly oversized so that it extended to the edges of the coaster) was a well shaded image that took about 2¾ hours to engrave. The cat was a line drawing of white against a black background. I inverted the colours and engraved the resultant PNG file in about 12 minutes. On balance, I prefer the heavily stylised image of the cat and feel that it makes for a far more artistic image.
I have also engraved images onto these pieces of glass using the white paint and Norton technique and the results have been excellent. All comments are welcome.