Can shellac (Bullseye in this case)be used on new wood as a primer before painting with an oil paint? I used shellac as primer before brushing-on an oil-based color paint. I then used a 2nd color (this was a spray paint)for accents. The 2nd color immediately "crackled" - a nice look but not what I wanted. Is shellac a primer? Why the "crackle"?

Yes you can use shellac under oil based paint as a primer. The spray paint may have had solvents in it that caused it to crack over the other paint.

I am a Paint Rep for the Sherwin-Williams Company. I recently went to a job where Shellac Primer was used on walls and trim because the homeowner was a smoker. Our top-of-the line interior Flat paint was used on the walls and Semigloss on the trim. What looks like "crackling" has occured throughout the room. More prevalent on the walls then the trim but on both surfaces.

I believe it was because the Shellac primer was not dry before the topcoat was applied. Have any suggestions? I may have a picture up soon.

The problem is not the shellac primer but in the first finish coat and the spray paint. The spray paint has solvents in it that can cause this to happen in some cases, sometimes you have to wait for the paint it is applied over to cure a certain amount of time so it does not cause it to crack/wrinkle.