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A Gunsmith’s Guide to Metal Prep for Baking and Bluing

By Eric Kiesler

Prior to bluing or the application of a bake on coating, a steel surface must be properly prepared. In either case, at a minimum the work piece must be thoroughly and completely degreased. There are many acceptable ways to degrease steel parts, so long as no residue remains the method used is not critical. We typically recommend TCE (#083-060-024) for degreasing prior to the application of Brownells Baking Lacquer (#083-046-801) or Oxpho Blue (#082-024-004). The TCE in the spray can is preferable as it allows you vigorously spray the surface, start at the top of the part and hose it down to the bottom chasing the grease off. Incidentally, we offer a “how to” DVD (#084-000-238) on spray-on coatings. Prior to hot caustic Bluing (#082-005-007) the parts are immersed in a heated detergent bath using Dicro-Clean (#082-005-008) because (like TCE) we know it will have no adverse after effects or residue that could cause problems later on. Once the degreasing is complete, the part could be blued or coated, however, with bake on coatings, adhesion is greatly enhanced if the surface of the parts are roughed up. This can be accomplished by sanding them with a fine abrasive cloths, sand paper, Emory Cloth (#657-110-120) or by abrasive blasting. Abrasive blasting is preferable because it will typically reach areas that sand paper might not. For the Gun Kote (#083-051-001) brand of bake-on finish aluminum oxide (#084-206-060) must be used as the abrasive blasting media in your abrasive blaster. For our other bake on coatings (and even Aluma-Hyde) sand or glass beads may be used in the blaster. If you do abrasive blast the part (highly recommended), it should be degreased afterwards because the blasting media may have contaminants in it. You don’t want to coat a highly polished part since shiny metal resists the coating, but a highly polished part could certainly be blued.

The best approach I’ve found to do good metal polishing requires that all polishing be done almost completely by hand. Hand polishing while time consuming, preserves the original lines of the part better than polishing with a buffing wheel (#089-407-000). That is not to say a fine polish job can not be done with a buffing wheel, it certainly can. To come close to matching a hand polish with buffing wheels requires a large selection of wheel types, (#032-638-500) & (#088-061-500) and a considerable amount of skill. For most, mastering hand polishing is easier than mastering wheel polishing, and in my mind an expert polisher can do both.

To get started hand polishing, you’ll need some basic tooling: metal files (of various shapes and styles), a File Card (#537-020-002), abrasive cloth/paper in grits starting at 80 and up to 600 (or higher), and sanding blocks. The blocks you make up yourself out of scrap hardwood. I have a selection of blocks of all shapes, rectangles, wedges, concave blocks, and some dowels of various diameters. Depending on the contour of the surface I will select one block over another. Ultimately, you want a flat, hard, consistent surface to back up the sand paper; using your hands will result in a wavy surface finish.

A damaged or rust pitted surface may initially need to be filed. An expert polisher is capable of repairing a damaged or rusted surface to the point that it is nearly indistinguishable from its original undamaged condition. To achieve this effect, you must match the original factory polish marks in terms of size and direction; some strategizing is in order. If there is no undamaged portion of the finish, you may want to examine an undamaged version of the piece you’re refinishing. The idea here is to estimate the grit of polish the factory used and the direction of the polish marks (scratches). Initially, we want to select a grit size just smaller than the largest scratch we are trying to remove. In the case of gouges or rust pitting the draw file is the “grit” to start with. When filing the file should be carded often to avoid chip load, scrubbing the file with File Chalk (#080-705-006) will also help clear chips. Some Gunsmiths like to saturate the abrasive paper and steel surface with ATF or motor oil to help clear chips and extend the life of the paper.

File marks are to be removed with 80 grit paper, and the draw file is the coarsest “grit” a polisher uses. The 80 grit is polished perpendicularly to or at a 45 degree angle to the file marks. Once we have polished out the file marks with 80 grit paper, those marks (80 grit) will be polished out with a finer grade of abrasive paper (perhaps 120 grit). Prior to moving on to the 120 grit abrasive, the surface should be inspected for any traces of the file marks we were attempting to remove with the 80 grit paper. If any file marks are detected, go back to the 80 grit. Each time you move up to a finer grit, the direction of polish will again be perpendicular or at a 45 degree angle to the previous polish marks. There may be exceptions to this rule depending on the area being polishing. In any case, the scratches from the previous coarser grit must be removed; checking with magnification can be extremely helpful here if you have a magnifying glass.

Most of the major firearms manufacturers for economic reasons typically do not polish their firearms any finer than 320-400 grit and it’s usually done with a buffing wheel. The Gunsmith is of course free to polish as fine a grit as he or his customer desires.

Here are a few examples of finished guns done by the newest addition to our Gun Tech group, Monte Crain. As you can see, all of the work put into prepping metal surfaces pays off when your guns turn out as well as these.