In article , "Ian White, G3SEK"
writes:

In Europe there's a gadget called a Dalo resist pen which is made
specifically for hand-drawing on PCBs. It has a fine fibre tip and very
thick, quick-drying ink. It's very expensive for what it is (namely a
not very good fibre-tip pen) but with care it can be quite effective.

As many people already know, the Staedtler marker pens (waterproof/
wasserfest grade) are excellent for touching-up photo and iron-on resist
patterns, but they're not as good as the Dalo for filling large areas.

I'll add something from the machine shop that is probably in
the UK as well: Marker lacquer used to make marks on metal
about to be machined. Over here it is usually a deep blue and
is very dilute lacquer, obvious from the acetone odor. Various
brands, some are available in red or green (not good colors).
Scribes nicely. Brushes well with small brushes available from
craft stores.

From the drafting department of old: K&E ink pens, the two-part
cylindrical, concentric ones. Those will hold dilute lacquers and
there is a pen holder that takes the nibs. Must soak them in
acetone after using since the capilliary clearance is tiny. With
practice those pens can draw straight lines but any dilute lacquer
likes to migrate to the straightedge...:-)

Office Depot and Office Max chains over here carry the Sanford
"Sharpie" pens (permanent marker type) whose ink is ferric
chloride resistant. I find it difficult to maintain a fine nib on those
for small foil lines and prefer a small brush. Mileage varies.

I once tried acetone-diluted liquid rosin as a resist, had mixed
results. Nice odor combination while doing it. :-)

As always, with any kind of resist, the unetched copper surface
must be clean and oxide free, smooth in order to take the resist
evenly.

Len Anderson
retired (from regular hours) electronic engineer person