Metal Blackening

According to this post, cast iron can be colored in the same way as steel, but it takes longer.

http://yarchive.net/metal/bluing.html

Hello MOONLIGHT!

This only my way of thinking about blackening metal: make a mild, 5 to 10% chlorhydric acid solution, dip the metal and let rust for 30 minutes to 2 hours, let dry for at least 1 day the metal. Prepare a 5 to 10% Tannic acid solution and dip the rusted metal into the acid and let in for 10 to 15 minutes. Take of the piece and check the beautiful colour of your metal.

Let me know how you like your piece in reality, and I follow up for better results. Watch acids. Use gloves, goggles, and other protection, and aerate the place.

Wish you a black weekend, Gil.

dear gill .

in brief ,we have 50 pcs of investment casting that we have to color black,but when we did a process over them we found 10 pcs turned light reddish or you may say it

a black reddish look (different from other black pcs). i was thinking that this is the problem of cast iron content in it . but one of our member told that there is not any efffect of since cast iron and steel both have same solution (acid)to do with.

can u plz suggest me wat will be the reason of 10 out of 50 turns in reddish look.

thanx

moonlight

Hello MOONLIGHT!

Sorry! I don't have any suggestion because you don't tell me clearly what you did. Concerning acid treatment, and the following step(s). Explain what you did and I will come back but I don't like to guess, Gil.

gill actually we are doing our steel product black thru oxidation we do it with carefully in a compound of sodium hydroxide,sodium nitrate and sodium nitrite..but the results are not upto the satisfaction since in a lot of die cast pcs approximately 20-30% pcs turn red brown while other remaining black.so the rejection rate is more .can we change the compound or do u have any solution for it .

waiting for urs reply.

moonlight

dear gill .

in brief ,we have 50 pcs of investment casting that we have to color black,but when we did a process over them we found 10 pcs turned light reddish or you may say it

a black reddish look (different from other black pcs). i was thinking that this is the problem of cast iron content in it . but one of our member told that there is not any efffect of since cast iron and steel both have same solution (acid)to do with.

can u plz suggest me wat will be the reason of 10 out of 50 turns in reddish look.

thanx

moonlight