I'm rod coating salt prints (I have seen this happen with kallitypes too though) and when I coat the silver it leaves a faint outline wherever the solution is spread initially. I have tried all sorts of methods of coating, humidities when coating, etc and cant seem to knock them out completely. I've attached a picture to show what I mean, you may need to enlarge it since it is fairly faint. The solution is just silver nitrate in distilled water. I've also tried adding a drop or two of wetting agent and it's been hard for me to tell if it makes much a difference or not.