Greetings!! I work in the bakery equipment industry and am presently doing some research and development work with our bakery trays and pans. We have recently changed from using tin-plated to aluminum coated steel sheet because it withstands higher oven temperatures, but also find that it reflects too much heat. Now I am looking at a chemical dip process that can be used in a single pass process line that will easily and effectively darken the aluminium coated steel. The maximum process time would be up to 3 minutes due to physical dimensional restrictions of the line. The aluminium coat is approximately 20 microns thick. I have tried various solutions the first being a hydrogen fluoride based solution with reasonable results, but I do not like the idea of having to work with HF. I also tried using a caustic based formulas but they ate most of the aluminium away and formed a precipitate residue (smut) on the surface. In these cases a darkening effect occured but this was only due to a reaction with the mild steel base material. So now I am looking further afield to see if anyone can make any further suggestions as to methods and/ or chemicals that I could try to achieve a dark grey colour without attacking the base metal. Thankyou for your time and any input would be greatly appreciated. Yours sincerely, Fiona Gliddon. ----- chemweb: A list for Chemical Applications of the Internet. Archived as: http://www.ch.ic.ac.uk/hypermail/chemweb/ To unsubscribe, send to listserver@ic.ac.uk the following message; unsubscribe chemweb List coordinator, Henry Rzepa (rzepa@ic.ac.uk)