I tried the method outlined by Bob Loveless. Had to go to a different company for the chemicals. I don't know if my problem was a too-weak UV light, or having 2 left hands, or just being stupid, but I got only 25% success. Talked with a knifemaker in PA who used the method with total satisfaction and bought a different developer. Exchanged quite a few e-mails trying to get my process right. Wound up with a gallon or more of various photo chemicals and never did achieve even 50% success.
Went back to the electro-stencil etch and, other than when I tried to stretch a stencil past its limit as Lin said, I've had 100% success.
Got my latest stencils from Ernie Grospitch and they do last longer than the flimsies I bought years ago.
Ernie also passed on a tip: when marking damascus, etch the mark on the polished blade. Then paint the mark with finger nail polish. Let the nail polish cure really hard (UV will speed this up somewhat. Rub the nail polish off the blade surface with the same grit you used for the pre-etch polish, backed with a hard block so you don't get down into the mark. Then do your damascus etch. The marks stays sharp and protected. Take the nail polish off with acetone as a final step.