2-Piper
The Boric acid etch comes direct from Angier's book and I don't think I do anything out of the ordinary.
I use a stainless steel bath, dissolve boric acid powder in distilled water (clean rain water would probably do) to about 5-10% w/v. This gives a saturated solution at about 50-80 deg C.
I grease the inside of the tubes, plug with hardwood dowels, carefully degrease the outside with whiting (you must do this thoroughly as the boric acid will not work well with a contaminated surface and once oil contaminates the solution one really has to throw it out and make a new batch).
I then warm the solution to 60-80 deg C and lay the barrels in the solution for between 30 min and 2 hours.
It is very gentle but if the surface is clean it quickly mattes the surface showing the full pattern of the damascus. After a bit longer, carbon from the steel starts to darken the surface and can make the pattern harder to see but a brush with a gloved finger wipes it away and all becomes clear again.
When the pattern is distinct over all the surface, rinse with fresh tap water, remove the plugs to check the bores are still dry, if not dry out, re-plug, degrease and start your browning.
The solution does not last for ever and needs replacing once you notice that the etching is getting too slow.
