There are many sophisticated solutions ayailable but you can use a solution of table salt (Kosher salt may be better) in water with a drop or two of dish washer to each cupful. Dissolve as much salt as possible in half a cup of hot water and allow it to settle and cool. Carefully pour off the clear solution and add it to at least an equal quantity of clean (preferably distilled) water and add a drop of dishwash (to help wet the etch pad). This solution works on stainless and carbon steel and is suitable for vinyl stencils. I used it with Marking Methods stencis for some time and had no problem with it.