Niobium Anodizing

Howdy Folks, What DC voltage range is required to yield the range of
colors possible for niobium? tia Carl 1 Lucky Texan

Your best bet is to get in touch with Bill Seeley, Reactive Metals.
He knows everything there is to know about reactive metals. e-mail: web:

Have fun with your Nb. ‘Red’

Dear Rebecca & Carl, Our standard anodizer is 0 - 150VDC. Most of the
most common colors are in the 0 - 100VDC range. I have anodized to
over 350VDC in the lab. Amperage should be a consideration too. Low
amperage is all that is needed in jewelry applications. Our anodizer is
3 amps. 10 amps will do a bike frame. Bill

For me, the practical range is in the 2-80 volt, mostly 4-30v. You
are building an increasingly thick transparent oxide layer on the
surface. This oxide layer is the thickness of various wavelengths of
light and causes an interaction with the reflection of the light to
limit the reflected light waves to specific colors. As you build
thickness the color goes silverish again and if you increase voltage
you can get into a repeat rainbow, called second, third etc. order
colors which are similar to the first round of colors.

One of the things we do not think about in changing AC to DC is that
AC is usually measured as RMS voltage (root mean square, I think), not
the peak voltage. The peak voltage may well be 15-30% greater than
the RMS voltage. When I do the anodizing, my RMS AC is in the 0-130
volt range. When you rectify this, you get 50% of the voltage, but you
get the peak voltage. One of the things I like about straight
unfiltered, unsmoothed rectified AC is the ripple of the voltage .
Most of the voltage is less than 85% of the peak voltage so you can
paint the color. If you leave the electrified brush in one area, that
area will develop the full oxide layer, but you see it come up. One
bit of advise, the wet color is NOT the same as the final dry color
because of the effect of the added thickness of the water.

Have fun. If you ever have a tough question or need supplies, Bill
Sealy (sp?) of Reactive Metals is THE expert on Ni and Ti use for
jewelry (online at I hear he is happy
to give advise over the web or by phone. Usual disclaimer, no
relationship, just took one of his great workshops.


Thanx Bill and Marlin, I recently bought a used autotransformer
(mounted in a box with a handle!) off ebay and was concerned that I
may need a 1:2 step-up power xformer to get 200VDC. The output of this
variac is rated 140 (10A) and with the true peak voltage issue Marlin
mentioned I should be good to go! Just need to get bridge rectifier
and a few more goodies and I’ll be calling you up Bill! Assuming I’m
prepared to remove the oxide layer, there’s no reason titanium can’t
be annealed in a kiln is there? Will HF or that stripper Bill sells
take it off or should I expect to be using files,wire brushes etc.? (I
know, just wait and see). Carl 1 Lucky Texan

For me, the practical range is in the 2-80 volt, mostly 4-30v.

I use more in the range 40 to 150 volts. 150v or more for a rapid
application and a variety of colours. I prefer to avoid the lower
voltages as they are more prone to being spoilt by touching, as the
small amount of finger grease can alter the lower voltage colours
whereas the higher voltage colours are less affected by touching. Teal
and other greens start (depending on the size of the workpiece) about
100v. Our mains here is 240v.

Remember, voltage is relatively irrelevant if you are using a variety
of workspiece sizes. Just watch and see.


You are going to anneal Ti in a kiln? You will hate yourself. The
oxides that build up during an extented time at high heat are very
hard and thick. The alpha enriched layer will extend deep into the
metal and all have to be removed for clean colors. You can do it, but
it will be the grinder that will save your day. It will take a lot of
time. Hope you don’t plan to get paid for this work. Bill