I used the resin to create a harbor water scene for a model railroad. Resin has been cured for a few months while working on other parts. I need to go back and do a water ripple effect on top but notice I have lots of dust and building materials on the top of the resin. Some of it is sandy. What is the best way to clean this off without scratching the resin surface? If I wet my finger you can see it pick it up but if you rub it, it will scratch. The pour is about 3’x1′.