I was worried that the cost and being more friendly to environment, that it may not be as effective as I would like. I have an old rusty telescope I am restoring. It had a large gear 10" across with hundreds of heavily rusted teeth. I left it in a bath of evaporust for four days to be sure I gave it full opportunity to do its stuff. I pulled the gear out and the rust was " Completely" gone. I was amazed and recommended it to others who also work on antique large scopes. Love it!