Stainless, polyethylene, and polypropylene are safe to use with lye solutions of any strength. Lye will etch glass although slowly. As long as you aren't concerned with a minor amount of etching, you can use glass as well. If mixing lye with water, a large amount of heat is generated. The best way is to add lye slowly to the water while stirring. Cooling the solution in a cold water bath helps to keep the heat down. When I worked as an analytical chemist, I used to mix up five liters of concentrated NaOH solution on a regular basis. Wear PPE, especially a safety shield. to protect your eyes and face. Lye solution will readily dissolve skin.