I started with inspiration from a pre molded "rock" from petsmarter after i applied pieces of it using greatstuff i artistically arranged my sculpture. After the GS was dry i spent a good amount of time carving out spots to look like rock.
The next step was to apply the silicone. I used a paper plate and a Popsicle stick to mix up about 7 different colors of grey using a tube of white,black,brown. (you can skip the brown i didn't use very much of it at all) Use your fingers (wear gloves if you would like) and dab the silicone one creating thousands of little peaks, the dryer the silicone gets the stiffer it gets and the more texture it creates. Have a separate little spot on the plate for plain white and plain black, use this on top of wet grey to make highlights and shadows, it really makes it pop.
I did several coats making it very deep, i even rubbed a thin layer of black on top in some places, wiping it off the top of the texture and leaving it in the cracks.
After that just make sure it dries well and i rinsed the tank out with hot water a few times. You are bound to get some silicone on the glass where you dont want it, a razor blade will help you get it off but if your having a tough time like i was, there is a silicone remover you can buy at home depot.
Hope this helps, thanks for looking guys
