Gene, blacking of brass is easy. Get yourself a small quantity (a piece of fingernail size is enough) of potassium sulfide, K²S, from the pharmacy, commonly called liver of sulphur and sold cheaply (in Germany) for medical bath purposes, for instance, as skin cleaner for teenager (how about that?). Dissolve a very small amount in a lot of water, so the solution is only faintly brown, not more. Put in your degreased workpiece and watch it under good lighting. It will turn brown and then turn black, at which point you take it out quickly and rinse it under running tap water with scrubbing (old toothbrush). If it seems to be insufficiently black, repeat. The goal is to produce a very thin layer of copper sulfide on the surface (dead black). Longer application will cause the layer to become too thick and to peel off in tiny flakes or sheets. Depending on the alloy, It may help to etch the brass at first with hot citric acid, formic acid, acetic acid (concentrated vinegar), coffee percolator cleaner (sulfonic acid) or some other organic acid to remove the zinc on the surface, making the copper come out on the surface so the brass appears reddish.
No finishing afterwards as this will make the surface more dense and reflective. Best regards Peter Blodow gene heskett schrieb: > Greetings all; > > The new encoder wheel I made last night, by fiddling with the math that > determines the slot width until it has virtually no side wobble of the > 1/16" mill at the inner apex of the slot, makes me ask a question about > what is the best way to chemically blacken brass, hopefully with the > intention of preventing reflections from the sides of the cut in the brass > that might artificially broaden the effective aperture of the slot. > > So, how does one chemically blacken brass? > > Ideally something that destroys any and all surface gloss, leaving a dead > flat microscopic felt like finish. > > I considered paint, but at those angles of reflectance, even black paint > might as well be glossy white. Plus I don't have any other than some ebony > wood stain. ;-) > > Cheers, Gene > ------------------------------------------------------------------------------ Virtualization & Cloud Management Using Capacity Planning Cloud computing makes use of virtualization - but cloud computing also focuses on allowing computing to be delivered as a service. http://www.accelacomm.com/jaw/sfnl/114/51521223/ _______________________________________________ Emc-users mailing list Emc-users@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/emc-users
