Re: Capone's 1930 Packard on Craig's List

Posted by Owen_Dyneto On 2012/11/28 14:07:25

The general term for the process to make etched metal plates is "chemical machining" and I sold chemicals and provided tech service to this industry back in the 60s thru the 80s. The earlier method was to apply an acid-resistant silk screen ink image of the areas that were to remain at surface height and then subject the piece to a fairly slow, controlled etching process, followed by removal of the silk screen ink and electroplating if desired. The normal etchant was ferric (sometimes called "iron") chloride of a fairly high concentration (about 1.4 specific gravity). The higher concentration etchant gave a slower and smoother etch. In later years the silk-screen imaging method was replaced with "photo resists" which were coated on the entire surface and then exposed thru a photographic negative of the image with subsequent development, followed by etching and finally removal of the photo resist. The etched decorative panels at the LBJ Library, though not of brass, were done in a similar manner.