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What makes for a better black oxide?

We are in the automation business and we frequently send metal pieces to black oxide process but I have seen others companies that make a better and more durable black oxide finishing than our supplier, I think I would look for other supplier but I'd like to now what makes a better hot black oxide process? is it depends of the time, mix, or other things?

Jesus Noyola
Calvek - Mexico
2005

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First of two simultaneous responses --

There are many factors, all of which need to be under control, to do good quality black oxide, but is not really a very complicated process, and it should be possible to find multiple shops which can do good quality black oxide.

Jeffrey Holmes, CEF
Spartanburg, South Carolina
2005

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Kindly suggest how dark jet black colour can be obtained continiously in hot black oxide process (caustic based chemicals ,temperature is about 135 °C)?

Hem Tewari
manufacturer - Anand, Gujrat, India
2005

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Some shops do cold blackening as opposed to a true hot black oxide process, Jesus. This may be done for safety because black oxiding can be hazardous. Although cold blackening can be useful, in general the aesthetic value of the finish is not as good because the finish is actually a selenium smut rather than a true black oxide. Although quality can vary from shop to shop, my first guess is that the finish you like is true hot black oxide and the finish you don't like is cold blackening. Please see our FAQ on this.

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey