Howdy Mary!
Unlike bluing, which uses a heated chemical bath, it
appears that the usual way to color stainless steel
is through an electrochemical (electrolytic) process.
There is also a "titanium sputtering" process. These
seem to be the best ways to get a colored surface that
will not scratch off. You can heat stainless steel
with an ordinary oxy-acetylene rig and it will color,
but this will not produce uniform results.
Coloured Metal Concepts on the electrolytic process.
http://www.capelink.co.za/alt/cmc/
"Stainless colouring is produced by an electrochemical
process that creates a thin layer of chrome oxide on the
stainless steel. By varying the thickness of this oxide
coating, we at Coloured Metal Concepts can produce the
following colors ..."
Abel Co. Ltd. on the electrolytic process.
http://www.asia-links.com/biz/vsap/column.asp?columnid=42&companyid=127
"Lumina Color - A chemical coloring process is frequently
used for applying a color to the surface while retaining
the metallic beauty of stainless steel. This coloring
process offers excellent rust resistance because it not
only provides a brilliant finish, but because it is
integrated with the substrate metal."
Legacy Design Group, Inc. on the electrolytic process.
http://www.legacydesigngroup.com/techinfo.htm
"Permanently Colored Stainless Steel is produced by
immersing finished stainless steel into a hot chemical
solution. The chemical reaction increases the thickness
of the chromium oxide, the protective film on the steel.
Colors are produced as the film thickens. The oxide layer
is hardened by means of this specially developed process
giving it permanent color. This permanent color has the
life span equivalent to that of stainless steel itself."
B&M Finishers, Inc. on the electrolytic process.
http://www.bmfinishers.com/stainless_steel.html
"Colored Stainless Steel: The color is produced by an
electrochemical process that creates a thin layer of
chrome oxide on the stainless steel. By varying the
thickness of the oxide coating, colors ranging from
Champagne, Bronze, Blue, Gold to Black are achieved."
The Minerals, Metals & Materials Society has some
details on the on the electrolytic process.
http://www.tms.org/Meetings/Annual-97/Program/Sessions/TP315B.html
"FORMATION OF THIN COLORED FILM ON STAINLESS STEEL:
G.S.Gupta, Dept. of Mining, Minerals and Materials
Engineering, The University of Queensland, St.Lucia,
Queensland - 4072, Australia"
...
"Formation of colored film on type 304 stainless steel
has been studied using chromic acid and potassium
dichromate solutions. Permanent colors have been
obtained using immersion and electrolytic (potentiostatic)
methods. The effect of different parameters on the
coloring process including temperature, coloring methods,
solution composition, stirring, surfactant etc., have
been noted. Moderate temperature of the solution,
electrolytic method, use of surfactant and stirring of
the solution were found to enhance the coloring process.
A coloring solution which is strongly oxidized and acidic
in nature is recommended. It is advisable that after the
extended use of the coloring solution, fresh solution
should be used."
The Hwa Yang Stainless Steel Group talks of using
titanium sputtering for coloring stainless steel.
http://www.hwayang.com/titanium_sputtering.htm
"The process of PVD, or Physical Vapor Deposition of
titanium (Ti), onto the stainless steel surface provides
an abrasion resistant coating which is up to100 times
that of normal stainless steel substrate. Titanium
Nitride (TiN) coatings have been utilized in the tooling
industry to extend the life of drill bits, to reduce
friction and to enhance resistance to the effects of
corrosion."
..
"Titanium colored stainless steel is available in gold,
rose gold, rose copper, brass, brown, bronze, black or
charcoal grey."
If you need any clarification, feel free to ask.
Search Strategy:
Google search on keywords: "stainless steel" coloring process
://www.google.com/search?q=%22stainless+steel%22+coloring+process
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