It must be said that there is no right or wrong way to go about engraving, the burs you use depend on what you want to achieve, and every engraver will develop their own preferences for burs, so keep experimenting until you find what works for you, but in an effort to be helpful, here's my guide for a basic set up to develop shading in your engraving.
Diamond burs are great for highlighting areas and fine lines (I use 120 grit for most of those areas), green silicone for filling large areas, white arkansas stones are best used as a pre-polish on areas that you would like to show really dark (will need to polish further with a rubber) and the rubber burs are for the final polish (different grades/grits will achieve different results)
There is quite a difference in the grit size of burs, particularly noticeable in diamond and green silicone ones, for example diamond burs can range from something like 40grit (very coarse) to 600grit (extra fine), the coarser the bur the whiter (and more textured) your engraving will be. I have found that the burs that come with the cheaper rotary tools tend to be quite coarse (these are ok for some things but not ideal if you want to develop nice shading). Have a good hunt on the internet for dentistry, jewelery and specialist craft suppliers for good quality burs in your area, you will be amazed at what you can achieve with the right equipment (by the way, these are not hugely expensive *smiles*).
Do you find the edges of your engraving tend to chip? Some ideas that might help.
- Do try finer grade diamond burs. Diamond burs come in varying grits/meshes from 40 to 600 (the higher the number the finer the grit, just like sandpaper). Most of the cheaper sets of diamond burs (and the diamond burs that come with the cheaper rotary tools) are quite coarse and while they may be great to use for highlights they do tend to increase chipping when used near the edge of engraving. For general engraving I have found 120 grit is good, finer grits are great for producing slightly shaded (darker) areas in an engraving.
- Try using a different speed on your drill. I have found slower speeds tend to produce better edges (especially when using an inexpensive rotary tool).
- Chipping can be increased by any wobble on the bur, wobble can happen as a result of worn collets, worn bearings in the handpiece, or over-tightening of the bur in the handpiece.
- Try using water, a wet sponge with a tiny bit of soap added dabbed on the surface, very regularly (this works as a coolant, and will extend the life of your burs too) is commonly used. Do engrave your outline without water first (or the water will wash off your artwork).
- Worn burs contribute to chipping too... try a new bur and see if it helps.
- Do use a very light touch of bur to glass. Going over the edges again (up to 3-4 times) with a very light touch of bur on glass can tidy up pretty much all but the worst of chipped edges, do consider that this will extend your engraved area.
Holding your glass while you engrave
Here are a couple of little things I quickly made up to hold champagne flutes while I work on them, simple but effective.
This was made out of some rather grubby off cuts of polystyrene sheet that I had lying around. I cut it with a sharp craft knife and glued it together with PVA (white) glue, using wooden toothpicks to hold it together while the glue dried. The black cover is the bottom cut off a leg of a pair of track pants. I cover the back of the glass with cling film to aviod it getting scratched while I work on the glass, as an added precaution (this is probably unneccessary when using this type of form to hold the glass).
When engraving the foot of a glass I use this simple board, it is difficult to see but I have cut out a curved shape to help secure the glass (on the left of the glass in this photo), The base and small support section are cut from a fibre board purchased from a stationery supply store, the support is glued on and the black card is held on with double-sided sellotape. The glass is then stuck onto this using double-sided sellotape too. This holds the glass firmly enough to work on and still allows the freedom to turn the whole unit as needed.