You want to spread the ink very thin and evenly. I think I got my rubber roller from Olsens when I bought the ink but check your local hardware or home store for a wall paper seam roller or similar. They may be wood or plastic but should work better than a razor blade. If you can find a rubber one even better.
https://www.amazon.com/Rubber-...TG9nQ2xpY2s9dHJ1ZQ==
Pete