Scanning and Processing Black Scratchboard

The mottling in the first and second images is from the matte varnish that is sprayed on.
Adjusting the blacks helps remove most of that and  careful dust removal using the cloning tool can take out the rest.

Getting a good scanned image can take a lot of practice and experimentation. I'm still learning, but this is what I'm doing so far especially in achieving the rich blacks of scratchboard.
When I scan I use an Epson Perfection 600 scanner which will do prints and also negatives and transparencies. I always hit the reset button to take off any scanner adjustments to sharpness, color, or levels and do those myself later using a photo editing program (Photoshop Elements 11 which came with the scanner).

When I open the raw scanned image in Photoshop I first adjust the levels with the original artwork right beside me to compare. I try to get the blacks as dark as I can without losing any of the lighter values in the image. I do the same to the white levels - get them white without losing any of the subtle grey values near them. If it is a black and white image I also strip out the colors using the desaturate feature.

Then I start going over the blacks especially doing dust removal with the cloning tool. It takes a fair amount of time to do this right. I zoom in quite a bit on the image to be sure to get it all. I get a bit obsessive in this stage to get as much as I can. At this stage I could also remove any smudges in the dark areas and also transfer lines that still may be there.

Once I have the image the way I want it I may sharpen it a bit - but not too much or the subtle areas will be lost. I also add a layer and tint it to 5-7% transparency with an olive color to bring back the warmer tones in of the scratchboard.

If I want to print the image I usually have to run a few test prints and make a few more adjustments to get the print matching the artwork - again with the original artwork right beside me.
That is my process at this time. It works pretty well for me so far. I got a lot of tips from the wetcanvas scratchboard  forum, and especially Cathy Sheeter who is one of the moderators for the forum.