Friday, October 21, 2016

Bluing or Aging Plated Nuts, Bolts and Screws

Why would you do that, you ask?  Well, a while back I was making something and I needed a screw to fit, and to look right it needed to be blued, but the commonly available screws are all zinc plated so they resist rust, and zinc won't blue.  Or, let's say you have a something (piece of furniture, tool, whatever) that needs a new screw or bolt, but you want it to match the look, or just need it with a dark finish instead of shiny.

There's an easy way to get the plating off, but you have to be careful: acid.  Very careful, in fact, because this stuff is dangerous, you don't want to get it on you, or inhale the fumes.  So, number one:
  • Do it someplace with good ventilation.
  • Use eye protection.
  • Wouldn't hurt to wear gloves.
  • Have some baking soda dissolved in water around; if there's a spill you can neutralize it, and when the process is done you use it to kill the acid on the part.
  • When the acid is eating the plating, it produces hydrogen gas.  It being highly flammable, make sure there's no open flame or other ignition source around.  I've never had this ignite, and I hope to keep it that way.
So, what acid?  I use muriatic acid.  It's easy to find (hardware stores, pool supply stores), and inexpensive.  I think a gallon -- the smallest bottle I've seen in said stores -- goes for about eight dollars, and if you keep it capped tightly it lasts forever.

The process is simple, demonstrated here with a machine screw.

You need something to put some acid in, deep enough to cover the piece (I use a hard plastic cup), and some steel wire.  Make sure the wire doesn't have any oil or grease on it.

Wrap the wire around the threaded portion, make sure it can't slip out.

Dip the screw into the acid.

You'll start seeing bubbles almost immediately.  If it's hot, and the acid warm, happens faster, if things are cold it'll take a bit longer.  When the bubbles stop, the plating is gone.  In warm weather, on a small piece, it'll only take a few seconds; here it took about fifteen before the bubbles stopped.

Take it out of the acid, and put it in the baking soda & water mix.  That only needs a few seconds.

Now I'd suggest washing it with a little soap, both to kill any traces of acid that might be hiding in the threads and to flush off any baking soda so it doesn't interfere with the bluing.

Fresh out of the rinse, still bright but it looks a touch frosted; that's from the acid lightly etching the surface.  Ready to blue.

Here we're using a cold blue, such as this.  'Cold blue' because you just brush it on and it requires no heat*.   I'm using Van's Instant Gun Blue, because that's what I have handy.  Good stuff, hard to find at times.

You can leave the screw in the wire as a handle, or use a glove to hold it, both to keep the stuff off your hands and to keep your skin oils off the steel.  Use a cotton swab to wipe the blue liquid on.  The instructions are generally something like 'wipe on, let sit x minutes, wipe off'; check your bottle for specifics.  I've found for best results with most of these it's
  1. Brush it on.
  2. Let sit a couple of minutes, wiping a little more on if it starts to dry.
  3. Wipe it off.  If not dark enough, burnish it lightly with 0000 steel wool, then brush some more on and give it a couple of minutes.
In this case only took about a minute to get a nice blue color

When dark enough, dry it off and then give it a heavy coat of oil, any oil will do, and let it sit on a safe surface for at least an hour.  That'll both help set the color, and prevent rust.
Wipe the excess oil off, and it's done.

This is fresh after oiling:

The other way to finish this after the plating is off is to rust it.  Done right it will give a dark, old-looking finish that lasts well.  I should note that rust bluing is a process done on fine firearms for many years, but we're not going to that level.  For this, after you take it out of the acid, just rinse it with water to flush off the acid, and hang it up where nobody will bump into it.  If the humidity is high it'll start rusting very quickly.  When it's covered with light rust, hold it with a glove and use a wire brush to remove the rust; use a light touch, you don't want to take the surface down to shiny, just knock off the loose surface flakes.  If the surface is evenly darkened by the rust, you can stop.  If it's uneven, or the surface is still bright, wet it and let it rust some more.

When you've got the surface you want, oil it to stop the process and darken the surface.  If it's a bolt or screw you'd  use on furniture, I'd suggest wiping it heavily with boiled linseed oil.

Let it set for about an hour, then wipe the excess off and let it dry (anywhere from a few hours to a day or two, depends on temperature and humidity).  That'll keep the steel from rusting, and if you're putting it into wood it won't soak in like a regular oil will.

The other thing you can do to finish a screw is to, after the color is set, make sure the surface is wiped dry and then wax it.  Something like Johnson Paste Wax works very well.  And if you've got, say, some Turtle Wax, that ought to work, too.  Put a light coat on, let it dry, then buff the excess off.  And two coats wouldn't hurt.

*Standard bluing is called 'hot blue' for a reason.

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