No cost, no registration, no passwords -- just aloha, fun & authoritative answers
(as an eBay Partner & Amazon Affiliate we earn from qualifying purchases)

Home /
Site 🔍
pub  Where the
world gathers for metal finishing
Q&As since 1989


Black oxiding of cast steel and A2 & D2 steels

greystone banner

Q. I'm doing chemical blackening on steel using the hot process at the moment I'm having a torrid time with any form of hardened steel or heat treated material at best I get grey but with longer immersion times it turns a rusty orange colour. Normal mild steel is nice and black as for the rest it's lots of brown.

Peter Quadling
Job Shop Owner - Benoni Gauteng, South Africa
March 3, 2022
    privately respond to this RFQ   ^
Ed. note: As always, gentle readers: technical replies in public and commercial replies in private please (huh? why?)

⇩ Closely related postings, oldest first ⇩

Q. I am looking for information on the blackening of different kinds of steel. I am wanting to speed up my process so that I can have a good turn around time for my customers. I know that cast is harder to black along with A2 and D2 steels. If there is something that I might not know, that may help with my process, any pointers, advice or help I would greatly appreciate it. Thank You.

Stacy L. Hitt
Southern Michigan Black Oxide - Jackson, Michigan

A. Ferrous alloys with more than 1% carbon or alloying components like chromium or nickel often require being run through black oxide solutions designed for Stainless Steel. You should also consider Room Temperature blackening chemistries for these applications.

Scott Papst
- Inman, South Carolina

H13 Steel turning BROWN with the black oxide process

Q. I'm searching for some information regarding the hot black oxide procedure with H13 steel. Does anyone know why 90% of the time the results with this particular metal seem to come out a dark brown instead of black. We have tried many different tests to determine this and seem to be hitting dead ends. Is there a better blackening process for this type of steel? Are we following the procedure properly? Is the bath possibly too hot? Thanks for your help.


Heather McKenzie
Technician - Russia, Ohio

A. I run a black oxide finishing system on firearms and find that temp is critical between 136°C and 141 is the optimum. Browning occurs above 145 I have found----a dead giveaway is a green tinge in the bath solution. This shows a destruction of the stabilising agents in the bath. Check your thermometer for accuracy. Hope this assists.


Allan Bennett
- Hobart, Tasmania, Australia.

Black oxide on H13 tool steel

Q. I have been searching for two days now (the internet doesn't always know everything) for a simple answer to this question. My background is not in metal finishing, but rather R&D design and my repertoire on coatings isn't as up to par as I'd like it to be.

We have a small assembly being readied for production here that uses hardened H13 tool steel and (due to the relatively high chromium content) refuses to take a manganese phosphate coating. At a previous job black oxide was used whenever phosphate would not suffice, but we are not currently equipped to do so here. My question is whether or not H13 will take black oxide, and if so, which class should be used? Everything I've read only refers to mild or low carbon steels but none that I have found reference tool steels.

Ian Walters
Product Designer - Berryville, Arkansas
January 21, 2010

A. Over the years I have made nearly hundreds of small gravers out of tool steel and I have always blued them to cut down glare and make them stand out against the work piece. I have used HSS, D2 and M7 but never H13. All of the tool steels that I have played with have always blued with the exception of M7 which turns the most lovely shade of purple I have ever seen in my life. I suppose M7 must have a lot of Vanadium in it. In the end it will probably boil down to just trying it and see what happens. If it does not blue its no great loss you will simply have to find a different coating and the company blueing it for you most likely won't charge you unless it blues. I would be willing to bet a case of beer that it does blue though or at least turns a blue, purple color.

rod henrickson
Rod Henrickson
gunsmith - Edmonton, Alberta, Canada
January 22, 2010

Blackening Process for D2 Tool Steel

Q. Can D2 Tool Steel be Chemically Blackened using alkaline Chemical Blacking Salts?

Lesley Clarke
manufacturer of Metal Finishing products - Tamworth, UK
April 18, 2017

A. Hi Lesley. Yes. We appended your inquiry to a thread where Rod H says no problem.


pic of Ted Mooney
Ted Mooney, P.E. RET
Striving to live Aloha - Pine Beach, New Jersey
April 2017

Q. Was not able to do hot blackening to H13 material. Need to increase time and sometimes its erodes the material. Could get brown colour but not black. What needs to be changed in process?

Durgadas Mokhadkar
- Pune, Maharashtra
November 10, 2017

(No "dead threads" here! If this page isn't currently on the Hotline your Q, A, or Comment will restore it)

Q, A, or Comment on THIS thread -or- Start a NEW Thread

Disclaimer: It's not possible to fully diagnose a finishing problem or the hazards of an operation via these pages. All information presented is for general reference and does not represent a professional opinion nor the policy of an author's employer. The internet is largely anonymous & unvetted; some names may be fictitious and some recommendations might be harmful.

If you are seeking a product or service related to metal finishing, please check these Directories:

Chemicals &
Consult'g, Train'g
& Software

About/Contact  -  Privacy Policy  -  ©1995-2024, Pine Beach, New Jersey, USA  -  about "affil links"