Involved people at OAB: Ciattaglia, Mezzini, Zitelli.
A big effort was done in the last years to study the best techniques to remove old aluminum from astronomical mirrors, increasing the cleanness of the glass surface before the new aluminization with minimum risk of chemical and/or mechanical damages. Initial experiments using excimer pulsed laser to ablate old aluminum gave promising results but the tuning of pulse energy to avoid damages to the substrate results so critical, to be considered unrealistic in a operation like the cleaning of a very large mirror. After the decision to return to more conventional chemical treatments, resulting in the selection of an optimal procedure, a prototype of mirror washing machine was built and tested. It permits spraying the proper sequence of chemicals on the surface to remove aluminum, clean, rinse and dry the surface without any direct mechanical action on the surface. An extrapolation of the results of the experiments to 8m mirrors shows that quantities, fluxes and costs remain in acceptable limits: the procedure can therefore be adopted as starting point for engineering a large dimensions machine.
At present, further experiments are conducted on small mirrors with the surface artificially contaminated by different kinds of dust, simulating different ambients.