I use 3 drops of glycerin to 1.5 oz. of 91% alcohol
Others recommend different percentages. You should play with it to see what you like IE
2 drops of glycerin to 1.5 oz of alcohol
3 drops of glycerin to 2 oz of alcohol
4 drops of glycerin to 1.5 oz of alcohol
The glycerin is vegetable glycerin. I got my first one at a health food store. Then I bought some at Amazon.
Note: I have found sometimes on tile the inks rub off real easily when dried. Perhaps if they are sealed this would not happen.