Q.How can this be cleaned, I've scraped some away with a putty knife, but at corners and edges the build-up is stubborn.

Hey Jerry-putty knives are for putty and will probably scrape your marble. Use a single edge razor blade and hold it at a 45 degree angle or less. It will cut right thru the soap film.Then use our mb-3 to get the rest and keep it mantained. Now if it is really bad get a stone refinisher to make your shower stall look brand new again and tell you how to keep it that way.

Find one at www.stoneandtilepros.com

Stu Rosen