Hi all,
I use both a marker pen and Dykem/Dymark it just depends on the size and how complex the job is .
For simple stuff where for instance I may only wish to drill 2 or 3 holes I use a marker pen as it is quick ,easy and can be kept in your pocket.
For more complex or larger work the dye wins hands down and any Engineers supply company should either have it or can order it for you.
Used to use copper sulphate to inspect Chrome plated rollers years ago as it won't plate over Chrome and you can see where the roller had worn through to the steel, I'm sure we used to add some acid to the solution to help it etch to the steel. Not nice stuff to play with though and only works on ferrous metals .
I agree that here in Australia the suppliers want to sell by the litre as that was all I could get without a special order, some model engineering suppliers have smaller lots but they can't post it as it is flammable.
The litre bottle has no brush so I purchased some swabs on EBay, this allowed me to decant some dye into a small jar like a medicine jar and keep the rest sealed up and the swabs work well.
Bearing blue (Engineers Blue ) is also good for smearing on Black Toilet seats !
Fun for the whole factory!
Ian