I need to dye some Birch ply panels black and red, are there any dyes that are more dense than others or is it just a case of applying the dye several times?
I have had good success with Chestnut's spirit stains on Birch ply.
Just keep adding more coats until you get the intensity you are looking for.
Chestnut sell small sample packs which you can use to try out the product and make sure that you are happy with the colour before forking out for larger quantities.
Thanks all. Since posting my question I spoke to a very helpful guy at "wood finishes direct" and, as a result, ordered some solvent-based dyes from them, plus some cellulose thinners, sponges and water-based varnish.
Apparently for a strong red the "starter" mix is 19 parts red, 1 part black and 20 parts thinners - but I'll be experimenting before going beyond the point of no return.