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Re: [Orchid] Blackening stainless steel
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patpruitt Thursday, June 21, 2007
   
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>     Does anyone know how I can blacken stainless steel? I can get some
>     discolouration by heating it, but I'm after a even, deep black
>     colour. 

    First question, what grade stainless are you working with? I work
    with type 316L stainless so these are my experiences, you may get
    different results with different grades of stainless. 

    Heating the stainless will give you the most lasting darkness, abeit
    its not a true black, but it is the SAFEST way to achieve a darker
    color on stainless that is not an oxide coating. I will also say
    that getting a true black on stainless is very difficult, its more
    of a blue black/dark grey that is achieved. 

    Rio carries a product called *Black Max* this will oxidize stainless
    but the coating will wear. Applying this to a heated piece makes for
    a more durable oxide, but difficult to control the evenness of
    color. This is good for surfaces that are below the main wear
    surface. 

    Now if you want to get serious, hit up www.epi.com they carry
    several products that work well. Both in a room temperature product
    and a heat applied product. 

    I will prempt the usage of these products by saying that both of
    these products should be taken very seriously in the personal health
    department, these are industrial products and should used with
    respect, so use adequate protection and ventilation, espeically if
    you are dealing with the acids involved. 

    Insta-Blak SS-370 is one product i use, its room temperature
    blackening agent and on type 316 stainless works well if applied
    correctly. Once again this product produces results similar to the
    Black Max and the oxide will wear. You will get more durable results
    by heating the piece (or solution) prior to application, or by
    cleaning the part in an acidic solution (muratic acid works
    decently, this strips the chromium oxide off the part). USE ADEQUATE
    VENTILATION and proper respitory devices with this product,
    especially if you use the acid bath prior. 

    Ultra-Blak 407 is a heated solution that you immerse the stainless
    into, you also have to prep the stainless with an acid solution
    (muratic acid works in a pinch) prior to clean the surface and get
    rid of the chromium oxide layer. this product works very well and
    has a good resistance to wear. The down side to this products is you
    really are dealing with some nasty chemicals that have a HUGE
    potential for personal harm. Once again, this is a very industrial
    product so use extreme caution. 

    With all these chemicals please consult EPI for proper
    health/safety/hazzard/disposal related issues. 

    With all these solutions you will get a more even color by bead
    blasting the part producing an even surface finish. 

    Now if your looking for a polished black on stainless, to date i
    have found nothing that can achieve this in a small setting. PVD
    coatings work well but are normally for large runs of product and
    are not condusive for doing single parts. Black chrome plating is
    another option that i have not yet done research on. 

    Other options are physical methods like powder coating, epoxies, or
    similar coatings. Good luck and be safe if you try any of these
    products. 

P AT 
www.patpruitt.com

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