Part of the problem is that whatever material you put on to act as a resist has to maintain your resolution when it's burned. Most sheet materials probably don't retain this property as well as something that goes on as a power or a liquid. Tapes have a tendency to burn to a rough edge, or in the case of Kapton, melt a tiny bit.
You might try using Kapton tape and see how it goes. It can only work if the adhesive retains its edge under the tape as it gets burned. Essentially you don't want the adhesive to be undercut/deformed under the tape surface. Kapton isn't cheap either.
We've been using a Rust-O-leum black paint (don't remember the line of paints), but it's the one that's used for painting high-temp surfaces like stoves. It's the one that was mentioned in the Instructable that we used as a starting point. We haven't tried anything else because it's worked well enough. One can is less than $4 and can probably cover at least a dozen square feet of board. We use two light coats and try it with a heat gun after each coat. We haven't even roughed-up the boards before hand if they're right out of the package. Wipe them off with IPA if you can't keep your filthy fingers off the boards before painting. IPA the burnt-off parts lightly with a cotton ball and etch.
You can cover a square food of board with two very light coats of paint for under $0.50, 10 minutes and a little practice.
The non-obvious part of this process is that you need a negative PDF to feed to the Epilog because the black area is what's removed. Two sided has been doable if you can align any two perpendicular edges on the cutter.
We typically measure the width of the chunk of board that we're working with and do the layout/tiling to that dimension. Not doing this won't give you "optimal" alignment results when you flip the board over to zap the other side.
If you don't like the results after it comes (hot) out of the laser cutter, take off the paint with solvent or steel wool and do it again.
Assuming that you've already eaten the sunk cost of the laser cutter, I'm not sure how you can beat the combination of COTS copper clad and about $0.35 for spray paint.
Again, the resolution isn't as good as with a pre-coated photoresist board, but 8/8 to 10/10mil is pretty good for about 1/4 the cost and about the same amount of time.
> > Question is: What could easily be used to coat a copper clad board that
> > will be resistant to the etchant (pick your flavor).
>
> I didn't send anything to be etched, but guys (& gals?), just take
> the question straight:
>
> What's the easiest etching resist to apply?
>
> It doesn't have to be a photo-resist, just something that will live
> through the etching process - an etch-block. Laquer? Auto primer? Asphalt?
>
> Once John applies it, then he can see what power and speed is
> required to reliably remove it. Even if it's a spray-on that tends to
> run, as long as it's not fused glass the laser should be able to remove
> it. He just seems to be looking for the easiest one to apply to the board.
>
> >There also seems to be a widespread want of something better, but I
> >haven't seen any solutions yet (still digging).
>
> Something better/easier than spraying or brushing it on? Of course
> there's dipping, but that's no better. Some sort of tape maybe? Is there
> a tape that will survive a trip through an etching bath? Of course, then
> there's the difference between cleanly ashing the tape (raster cut...)
> and having to edge cut it all and hand-strip it. If any remaining
> particles are small enough the etchant will undercut them, so there's a
> point where they'll be negligible.
>
> yeah, my kinda problem... Oh, and feeding the machine CorelDraw
> files worked much better than AutoCad files, I finally ended up just
> redrawing everything in CorelDraw (true single lines).
>