[SEL] Parkerizing, bluing, blacking, & browning iron

[Richard Allen]

Parkerizing, bluing, blacking, and browning of iron and steel use
chemical solutions that react with the iron of the steel alloy to form
extremely hard (on Moh’s scale they are around 7, which = quartz and is
considered suitable for gems) darkly colored insoluble iron compounds
that remain tenaciously attached to the surface. Plain old regular rust
is in this category and forms the actual brown finish originally used
on guns and other tools until around 1850 when developments in modern
chemistry made bluing easy. Parkerizing forms the hard and insoluble
black phosphate of iron, while the others form the various oxides and
hydroxides of iron that are diversely colored black, blue, brown, dark
olive green, deep red, and yellow. Another kind of bluing is from a
class of iron compounds called “iron Werner coordination complex ions”
and these are a very beautiful deep blue color chemically identical to
Prussian blue. 

My favorite finish is the nearly black metallic graphite luster color
and is the easiest to do. It also forms the hardest surface and resists
minor scratching and abrasion quite well. It is made from 5 pounds of
lye, 2.5 pounds of ammonium nitrate, and a gallon of water. You don’t
need to make up such a large amount if you don’t need to, just use the
same proportions. A United States gallon of water weighs exactly 8-1/3
pounds if you want to make up the solution strictly by using weight.
Although not poisonous in its final form, it is VERY dangerous to mix
and MUST be done using gloves outside while wearing goggles to protect
your eyes. SLOWLY add the ammonium nitrate into the water, stir, and
then SLOWLY add in the lye about ¼ cup at a time while continuing the
stirring. It will get very hot and if the lye is added too fast it will
explode from the steam that forms. Lots of ammonia gas will be
produced, too. After it is cool you can boil your iron parts in the
solution. It acts very fast to make the black finish but the longer it
is in the solution the thicker it will be. After boiling for ten
minutes up to perhaps an hour wash the parts off in cold water.

The standard Parkerizing solution is made from 365 grains of commercial
phosphoric acid “syrup” (also called orthophosphoric acid syrup), 22
grains of manganese dioxide, and a quart of distilled water. The parts
are boiled in the solution for 4 hours and then rinsed in warm water
for a few minutes followed by soaking in baking soda solution for a few
minutes to kill any remaining solution. Distilled water can be added
during the boiling to keep up the level if it loses more than a third
of its volume. A Jerry-rigged Parkerizing solution can be made from 2
tablespoons of phosphoric acid, a tablespoon of iron filings, and the
black pasty contents of one new “D” or “C” size zinc-carbon (not an
alkaline!)  flashlight battery mixed in a quart of water. The
phosphoric acid can be obtained from a paint supply store and is used
for treating steel before painting. The commercial acid is called Metal
Etch, but that stuff is usually pretty dilute. Parkerizing makes a flat
black or very dull dark gray color.

The brown color can be made by keeping the steel parts in clay-type cat
litter damped with weak salt or ammonium nitrate solution. This is just
plain old rust, so don’t get the idea that this is something fancy!
Every few days the parts need to be removed and then wire brushed or
rubbed down with steel wool to keep the surface from getting grainy.
When done the parts have to be rinsed off with lots of warm water and
after drying the metal can be protected with car wax, linseed oil,
floor wax, etc.

The deep blue color can be made by keeping the steel parts in a damp
pasty gruel made from pulverized oak leaves for a few weeks. I don’t
know if dead dry or fresh green leaves work better. A paste made from
green avocado tree leaves will also work. Like for making the brown
finish, every few days the parts need to be removed and then wire
brushed or rubbed down with steel wool to keep the surface from getting
grainy. When done the parts have to be rinsed off with lots of warm
water and after drying the metal can be protected with car wax, linseed
oil, floor wax, etc. Boiling in a stew of oak leaves and galls will
also work but I don’t have any specific instructions on how that is
done.

The commercial cold bluing solutions contain selenium salts and are
downright deadly if mishandled and selenium poisoning has no antidote! 
The ingredients to make solutions for the other colors are all pretty
hard to get and are dangerous as well, and consequently I leave that
stuff alone. 

Work and play safely (thanks, Rick!),

Richard Allen