Some years back i shoved an uncoloured brown egg in my 100w CO2, it bleached the brown off, gave me good light mark.
Fiber, however, completely ignores the egg. Just like paper or wood. Not even a single mark or wisp of a spark… Soooooo, i sharpied it 
And it worked marvelously.
I have a massive set of coloured felt tips (something like 100 colours), i figured i’m gonna rainbow the egg and engrave, just to find that pretty much any colour in that set is ignored, except for black… wth…
Results:
For next year i want to make an attachment for my D80 chuck rotary so i can squeeze an egg between centers to engrave all the way round it… some 3d printing and fiddling with 20x20 extrusion is in order.