Oxidizing is a technique used to achieve a contrast between the material and the engraved characters. Usually performed on brass or aluminum plates in trophy and plaque applications, it can also be done on many engravable gift items to enhance the overall appearance and make the copy more readable.
Oxidizing techniques are an area of considerable debate. Everyone has a technique that has worked for them at some time; however, few people agree on all of the fine points. Here are some basic steps that can apply to both aluminum and brass, along with a few do's and don'ts.
NOTE: SAFETY FIRST - Oxidizing solution is an acid. Follow the manufacturer's safety instructions, including wearing rubber gloves and safety goggles.
All of this sounds easy until you try it the first time. Engravers will get mixed results for several reasons. First, if the plate or gift item is diamond dragged, you may need to repeat the job to get a deep enough cut to take the oxidizing effect. This is not an elegant solution but it can help.
A little trick to help darken the oxidized area is to spray the plate with a furniture polish such as Pledge. This seems to darken the engraved area. I presume it is caused by the citrus oils in the polish but for all I know it could be magic. It's worth trying if you are having difficulty getting the look you want.
If you burnish the surface of some materials, such as a coated brass plaque plate, you may get different results with different cutter widths. Oxidizing a narrow cut can be easier than oxidizing a wide tool path. The oxide coating may not adhere chemically to a very wide stroke and the appearance may look spotty. Try a smaller cutter and repeat the job. Burnishing has an inherent problem in that the burnishing method may rub some of the coating you are trying to remove into the freshly engraved area. Although we cannot always see this, it may impede oxidizing.
Lastly, if you have an air compressor, you may try blowing lightly on the rinsed surface of the newly oxidized plate. This will help dry the area and minimize water spotting as well as keep you from rubbing the oxidized coating out of the engraved area.