For the most temporary of marks use erasable markers, like white board markers. These will wipe away with a paper towel, leaving no marks after firing. These may not last long enough for your purposes though.
The next set of temporary markers are the permanent markers. These are more durable and resistant to being smudged off the glass. Most often they will fire cleanly away in the firing. But there are occasions when they don't. So it is best always to remove the marks before assembly. Usually water will remove the marks with a little rubbing. If not, then a spirit based agent will be needed. Of course then you need to remove the mineral spirit residues. I normally do this with window cleaner as used by glaziers, with no additives.
The most permanent marks are done by the paint markers. These do need spirits to remove them, or they will get fired into the glass. The removal of the mineral spirits is as for the permanent markers.
|This example gives a range of colours. It is best to use contrasting colours and I use black and white almost exclusively|
Of course, the best method of keeping marks off the glass is prevention.
In so far as possible:
- Don't use permanent markers
- Don't use oil in your cutter.
Temporary markers are usually all that is necessary.
Oil is definitely not necessary, merely a convenience, in your cutter.