The basic idea behind the blued backs is the same as gun barrels, to prevent rust and add a little protection. This is achieved by “hot bluing” where linseed oil was applied to hot metal. The process works well; however, over time it’s been shown to wear. Personally, I’m a fan of the process but not wanting to reheat the metal I find “cold bluing” that uses chemicals works great and at this point I’ve reblued a few dozen backs.
The process is not complicated so I’ll do my best to keep the directions simple. The terminology however can be. I’ll call the back ridge where the toothed plate is installed the “Back.” The saw plate where the sharp teeth are is the “Plate.” The chemical we’ll be applying is often sold as a “rebluer” for guns or a “darkening agent or blackener.”
The process can be done with the plate still in the back or with the back removed. I would say if you need to take the plate out for other reasons, like smithing, do so before you darken it; otherwise you can tape it off.
To start off, remove the handle and expose the back. Chances are with the handle removed you’ll find some left over bluing. STOP! Think about how old that is, most likely over 100 years. Kind of cool, no? Keep your nuts in order! Insert a few jokes related to nuts!
If you’re going to remove the plate for smithing or replacement, do so now. If not, you can tape off where the plate meets the back. Wait and do that after you clean and sand.
Sanding, scraping, or soaking, everyone has a process they like. Most of the time I’m removing the plates and find it’s easier to sand them apart. The plate normally gets more attention as the smoothness helps its function by reducing friction.
The smoothness of the back however doesn’t affect function and therefore doesn’t need to be overly polished. I usually sand with 220, 400, and 600, and if the rest of the saw is really clean, 800. If you didn’t remove the plate, tape off the edge of the back and sand the plate. Don’t get hung up on the final grit, it’s more about the aesthetics. You engineers, relax; put your slide rulers and calibers away. Keep in mind that if you’re not taking the plate out of the back you should sand the plate and the back before you reblue. If you’re removing the plate, the sanding of it is not an issue and just needs to be done before assembly.
With the back prepared you need to remove any residue or grease before applying the rebluing or darkening agent. Take note: if you find scratches and aren’t happy, go back and sand again; most scratch marks are caused by skipping grades of sandpaper. As my 5th grade shop teacher would point out, dull 100 grit sandpaper is NOT 200; it’s just a waste of your time.
If you’ve ever painted metal or done body work, you most likely have used paint prep and know the importance of doing so. For most types of bonding with metal, cleanliness is important; skipping this step is not an option. If you don’t own paint prep, acetone works fine; you just need to watch streaking, and wear gloves and a mask. When you’re wiping down the back, if your rag is getting dirty, you need to get to a point when it’s clean. The issue being that any oil or liquid will affect the lay-down and chemical reaction. The wiping down with paint prep is just to remove residue from sanding; it’s not part of the cleaning process. Double check both ends of the back as they often get overlooked. Go back and fix any issues and wipe down again; when you’re happy, it’s way easier to address scratches and such now.
Ready to rock! Double check the tape for those of you with plates still attached. Also, check that the back is dry and streak free from your paint prep step. Get your rags or cotton balls out, plus the rebluer or darkening agent of choice. See notes below on supplies. Also note some will stain your skin.
The idea is to wipe on the darkener in one smooth stroke. Try not to blot or wipe back and forth. I’ve experimented with dipping and it works great; however, it uses a good deal of liquid and I find if you’re careful, wiping works great.
Most rebluers or darkeners I’ve used quickly react with the metal. I normally wet a cotton ball but a clean rag will work fine as well. The chemical reaction is quick enough that you’re just wiping on, not scrubbing. If you start to see streaks or other discoloration, resist the urge to wipe more on. The streaks are most likely residue left from your paint prep step.
Finish the one side and use a paper towel or clean rag to wipe off any extra. The finish will look dull, rainbowed, and darker than you wanted; that’s good. Flip the back over and do the other side. Remember to do the ends, then wipe off any excess.
With both sides done, use some 0000 extra fine steel wool. I buy mine by the roll and cut to length. Note I said CUT. Ripping steel wool reduces its effectiveness and creates more metal fragment and dust; work smart.
Buff the applied area until the shine comes up and you’re happy. Buffing does remove some of the applied finish so if it’s a little dark, just buff it a little longer. If after buffing you find things don’t look good, you can apply a second coat. Keep in mind that the chemical reaction lessens with each application. Also with the second coat, you should wipe off and dust first and feather on and off if you’re just looking to work a small area.
At this point you should be ready to reinstall or “Knock On” your newly blued back or grab sandpaper and start over. Let me know how it goes and if you’re having trouble with the directions.
List of supplies
Darkening agent: also used for rebluing guns and aging of brass. These are just a few brand markets that often require hazardous shipping fees, so buy local when you can:
• Antique brass darkening solution by WIS Distributors
• Birchwood Casey PSP Gun Blue
• Jax brand Iron, Steel and Nickel Blackener
Sandpaper: Brand of your choice. I normally use wet dry.
Cotton balls or rags: I get my cotton balls at the dollar store and a bag lasts me a few months.
Rust remover: Brand of your choice. If you find you don’t want to dip the entire back to prevent etching of the metal I find soaking a cotton ball and leaving on the metal works well.
Scraper: Brand of your choice. I use one with replaceable razor blades
Dental pick: Works well for cleaning an etch if need be. Be careful.
Steel wool: The finer the better. I use Liberon (oil free) grade 0000 steel wool sold through tools for working wood and on-line.
Other Safety items: Gloves, mask, and safety glasses, all of your choice. Also be smart about things; read labels and know which chemicals, like acetone, are nasty stuff; so cover any skin it will come in contact with and don’t use it when not necessary.