Cleaning Brass for Painting

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paint will stick better if items made of brass are properly cleaned before painting Paint does not like to stick to most kinds of soldering flux, and even if you manage to paint over the flux, you will soon find that the flux does not stick all that well to the metal underneath.  There are three common types of flux that are used in model railroading: rosin flux, greasy plumber's flux and zinc chloride in water flux.**   Rosin flux can be removed by soaking in acetone, lacquer thinner, or methyl alcohol or by washing in a patented flux remover sold by electronics suppliers.  Zinc chloride in water flux is relatively water soluble and will wash off in hot water. Plumber's flux can be washed off with cleaning solvent (Varsol) and the solvent in turn can be washed off with hot, soapy water.  Scrubbing, perhaps with an old toothbrush, is usually required and even then it is difficult to impossible to remove all the flux from inside tubes, cracks and crevices.  For a better and easier job, think in terms of your household dishwasher.  Larger assemblies are easy to wash in your dishwasher - just pop them in, add dishwashing detergent and turn it on.  For smaller parts, a tin can with the top and bottom cut out and a piece of 1/4" mesh hardware cloth soldered across the bottom makes an effective small parts washer inside your dishwasher.  If your brand of rosin flux is not completely removed by your dishwasher, try presoaking in acetone or lacquer thinner, but be sure to rinse it off with water before consigning the parts to the dishwasher. For even better paint adhesion, roughen up the surface.  Sanding with #400 wet/dry paper or medium steel wool is not out of the question but sandblasting (if you have the special equipment) or acid etching are easier.  Ten percent nitric acid is fast but requires special handling and the brown fumes that come off are poisonous.  Other people report success using hydrochloric (a.k.a. muriatic) acid or vinegar. Cleaned, etched and ten primed with a metal primer, your brass project is finally ready for painting. ** Liquid acid flux and acid core solder is never necessary in model railroading and its use should be discouraged.