Cleaning Brass for Painting

Question:

I am in the midst of working on repainting some stamped brass decorative products from one of my customers. They were stored for a long time and were coated before storage with paint in some areas and clear coating in others. They are very tarnished. I am talking about black in some areas. I was looking for ways to remove the tarnish and not the details before repainting.

I have had several suggestions from my painters, suppliers and others. One suggestion is to grit-blast them. If you then want to paint them, you are all set as the brass now has “teeth” to hold the paint, and if you want to clear coat them, you can polish them with beads in the grit blaster. Another suggestion is to use a liquid tarnish remover, but you will need to strip them first if you want to clear coat, so that you don’t get an uneven tarnish removal. A third suggestion is using a household cleanser and a toothbrush under warm water. The last suggestion was to use the “polishing compound” that is next to the car polish in the automotive supply stores. I don’t think it is as abrasive as household cleansers and shouldn’t scratch. The polishing compound has grit in it but it does not seem to scratch. S.V.

Answer:

I am sure most of those suggestions will work. However, they do sound more like kitchen or garage methods rather than industrial pretreatments. Some will be more labor intensive than others. Some will provide more consistent results than others. You want a consistent, pretreatment method. The classical method for pretreating brass for painting is: 1. Clean the surface to remove oily soils, grease and other foreign matter. 2. Remove paints and clearcoats using paint strippers. 3. Roughen the surface by sanding, blasting or phosphoric acid etching. Alternatives to phosphoric acid etching are wash primer pretreatments or chromate pretreatments.