I’m wondering how steel, such as commercial letter punches, is
blackened?
Thanks for any suggestions.
Pam Farren
There are hot black oxide processes that are often applied to tools
and other steel parts to act as a protective somewhat rust
prevenative surface but they are multi step industrial processes and
not suited for studio metalsmithing use. A very dark blue/black can
be applied with gun blueing solutions like these
Also there are tool blackening solutions like
http://tinyurl.com/yz3sr5h
Both of these types of patina need to be applied on a super clean
surface and then sealed to prevent rusting (oil or wax).
Jim
James Binnion
James Binnion Metal Arts
You can also “naturally” blacken it via oxidation with a really hot
flame (I usually do this over a coal fire). Most of my iron forging
work comes out pretty black, and for some non-forged steel jewelry
I’ve done, I use my coal fire to heat it up (I’ve also seen steel go
black with a torch). Unfortunately, this will probably also cause
some fire scale (which luckily comes right off during the heating).
Once you get it how you want it you’ll need to protect it as Jim
mentioned.
-m
My company used to do a hot black oxide for stainless steel in
house. Its not beyond the reach of a small studio but its not a nice
job.
The process - I’ll use the brand name of the chemicals I used - all
from Electrochemical Products Incorp. (EPI). MSDS’s would tell you
the active ingredients - I can tell you they are all either very
basic or very acid. I literally worn a rubber glove and a high
quality gas mask for a 12 hour day in a 100+ degree room - this is
the reason we not outsource the process.
-
Clean in a hot industrial detergent - Eclean at 200F
-
wash very well - the chemicals from each step do no play well
with each other - no explosions just detracts from the effectiveness
of the chemical -
etch the surface of the stainless - Epik at about boiling - if
you are doing mild steel you can use a simple etch like Hydrochloric
acid. -
wash very well
-
Immerse in boiling blacking solution (Eblack) for about 15
minutes - temperature must be monitored carefully. The boiling point
changes with the concentration and the need to keep the contention at
the right level for it to work. -
Wash very well
-
Seal with a light water based oil for stainless - for mild steel
I used WD40
Equipment list for my 20lb batch sizes set up for each step - all in
a dedicated 300 sq ft room with the biggest exhaust fan I could find.
Also equipped with water, nat gas, and waste water storage system
(all waste water was picked up)
-
digital thermometer, 5 gal enamelled steel pot, electric hot
plate -
laundry sink #1
-
3 gallon beaker on a propane camp stove - need glass as the Epik
will eat through a stainless pot in about an hour. Beakers were a
problem as they were breakable and boiling Epik was dangerous and
highly acidic - I had a pail of baking soda at the ready. -
laundry sink #2
-
30 gallon custom built steel tank with insulated sides and a
50,000BTU natural gas bbg burner hooked up underneath. It is
critical that the solution does not drop in temp when you dump in the
load. The tank needs to be oversized and with a good sized burner.
Its also a tank of saturated salt at the boiling point and it needs
to be very uniform temperature - it took me 3 hours to get the tank
going - this meant if I fired up the tank I was planning a full 12
hours of blackening.
What I learned - mild steel is way easier then stainless
If you can handle 300 lb batch sizes pay the pros - we pay $90 for a
300 lb batch. I could do about 40 lbs per hour ($12 per hour). For me
the only benefit to doing it myself was I could do small batches.
When I did it I offered maybe 40 products blackened - now I pay for
300 lb min batches and offer about 12 blacked products.
Let me know if you have any questions.
Jon Daniels
The Ring Lord Chainmail
Hi Pam
The basic way to blacken steel is to quench in an oil bath. This
method is not good for tools as it will ruin the temper. You heat
your piece of steel to a bright red colour, then quickly immerse in
oil swirling it around until the flame is gone (so do this in a well
ventilated area). You end up with a jet black matte finish that is
quite durable.
This a very basic blacksmithing technique and shouldn’t be confused
with the industrial process in which James and others explained so
well.
Thanks James, Mike and Jon for your help!
I’ve made a trip to the gun shop to try blueing, and will certainly
try using the torch as well. Jon, I appreciate your taking the time
to go through all of the “hot” steps. I agree it’s something I could,
but really don’t want to tackle!
Thanks again,
Pam
Newburyport
The basic way to blacken steel is to quench in an oil bath.
I recomment Linseed oil 
CIA
Hi,
You have to be very careful quenching in oil as it can burst into
flames. See this link, about a quarter of the page down:
Not only can it will and tons of smoke too. Your quite right there is
a bit of a safety concern here that one should take precautions.
Something I didn’t talk about in my post, so thank you for this. Also
great link, the super quench seems interesting.
Never tried that, being a shop teacher I’m pretty frugal and use just
old engine oil. Is there much difference, either in colour of
durability?
Working with chemicals is dangerous and can result in serious injury
and/or even death. Do not attempt to use these formulas, unless you
have been instructed in proper handling of chemicals.
If by blackening you mean “gun metal” finish the formula is
distilled water 1 gallon
iron chloride 160 - 180 grams
phosphoric acid(75%) - the same amount as iron chloride
hydrochloric acid - 4.5% by weight of iron chloride
copper-sulphate - amount equal to hydrochloric acid.
solution should be hot
for very dark finish - eliminate iron chloride, replace hydrochloric
acid with ferric chloride, replace half of the amount of copper
sulphate with potassium permanganate. solution must be boiling.
Leonid Surpin
My husband blackens steel in his scuptures regularly. His method is
quite simple, after he has a clean finish (polished and oil free) he
heats the steel until it turns uniformly blue, even heat, then he
mist it w/oil, make sure your ventilation is good and wear a
respirator! This is his final finish, not something you want to
repeat! ;=)
Lisa Hawthorne
lisahawthorne.com
If memory serves, I once browned a home-made knife by suspending it
in a closed container over some of bleach mixed with a little water.
This is actually a rusting process. When the desired color is
reached, the object is then cleaned with steel wool. The object
needs to be completely degreased before starting in order that the
coating be uniform. Simple, cheap, and safe.
John Moe
Pentaluna Jewels
http://www.etsy.com/shop/Pentaluna
I’ve browned fairly large pieces of steel by coating it with a
strong salt (table) solution and leaving it in a plastic bag until
it’s nicely rusted. Then finish it with steel wool as John suggests.
Make sure the steel is clean, though. Fingerprints will definitely
show if you handle it after cleaning with bare hands.
Makes a durable finish in an attractive russet shade.
RC