From: Louis Boyd <boyd@pegasus.la.asu.edu>
Subject: Re: Anodizing Aluminum
Date: 26 Apr 1997
Newsgroups: rec.crafts.metalworking

PYRO3@ix.netcom.com wrote:

>       A while back someone mentioned using sulfuric acid in the
> Anodizing process of aluminum. I was wondering what strength acid
> would be appropriate and about how much voltage/current should be
> used.
>       I have an aluminum faceplate from stereo power amplifier that
> had a bead blasted(?) smooth silver/grey finish, which I did not like.
> I used the Scotchbrite idea and got a beautifull brushed look on the
> raw Aluminum. I would now like to anodize it black.
>       Is there anything else that will augment this process, like
> agitation,heat, etc.?  Any ideas are much appreciated.

I've done some black anodizing in a "home shop" environment. These are
small parts used in optical instruments with the goal being to produce a
flat black surface.  I've used the sulfuric acid used for activating
batteries which is available at most battery shops.  I dilute this about
10 to 1 with water (be careful).  I use a plastic tank with a lead
cathode.  This doesn't get consumed.  The tricky part is in attaching an
aluminum electrode to the aluminum part to be anodized.  I put plastic
tubing over the electrode to keep it from being anodized.  I use a 48 v
12 A rectifier with a variac in front.  I set the current for around 1/4
amp per square inch.  As the anodizing progresses the surface resistance
of the work increases and the voltage has to be raised.  It doesn't seem
to be very critical.  The bath works ok at 100 to 120 degrees F.  15 - 20
minutes.  I then rinse in distilled water and put in the dye, which is
heated to 160 degrees f. I leave it for about 20 minutes.  Then 10
minutes in a sealer, similarly heated. Boiling water will seal too.
Professional anodizers will probably cringe at the above procedure.

The results are very good on some alloys, awful on others.  I have good
luck with 6061.  If I pick an unknown alloy from the scrap it frequently
gives dull brown or splotchy results.  Anodizing dosen't usually change
the surface of the metal much.  If it's scratched the anodized surface
will be scratched.  For a flat black surface, sandblast or lye etch
first.  Fingerprints show up like mad. The aluminum must be VERY clean
before anodizing.  Use rubber gloves. It protects against the H2SO4 but
mostly keeps the aluminum clean.

It's easier to take the piece to a professional if they don't have a big
minimum price.  Another good black finish is baking enamal as used by
some gunsmiths.  It's available from Brownell's.  It gives a gloss finish
but isn't as hard as anodizing.  It doesn't care about the alloy though.

From: Louis Boyd <boyd@pegasus.la.asu.edu>
Subject: Re: Anodizing Aluminum
Date: 27 Apr 1997
Newsgroups: rec.crafts.metalworking

PYRO3@ix.netcom.com wrote:

>            I was under the impression all it took was some acid and
> electricity. Had a feeling it couldn't be that easy. So, what is this
> dye? Is it a common chemical (for black) or do I have to buy it
> special somewhere? Also, what about commercial sealers. Do
> they offer a big improvement over the water technique? If so,
> where would I find them?

Many products which look like "plain alumininum" have been anodized.  The
anodizing process results in a clear film being formed on the surface of
the aluminum. The film is porous.  Dye can be introduce into the pores to
give a wide range of colors.  A sealer locks the dye in place.  I
obtained the black dye and sealer which I use from:

East West DyeCom, Inc
5238 Peters Creek Road
Building 8
Roanoke, VA 24019

703-362-1489
Fax 703-362-7425

http://www.roanoke.net/ewdc/index.html

The dye is manufactured by Sanadoz Chemicals Corporation and is called
Sanodal Deep Black MLW Granules. It's a powder. To use it mix it with
water.  If spilled it it makes an awful mess.  I don't know who makes
the sealer or what's in it.  It's a liquid and is diluted with water
before use.

>            Of course I will practice this on scrap first, but I do not
> know the alloy used in the face plate. If it comes out poorly, is
> there a way to reverse the process?  As long as i've not sealed
> it, does it come off with some other chemical?

The reason for going to the trouble of anodizing is that it is very
hard to remove.  The coating is much harder than the aluminum underneath
although it is thin.  I doubt that you could bleach out the dye even
before sealing.  Sanding or grinding has the problem that once the base
aluminum is exposed it cuts much faster than the remaining coating.
Chemical removal would probably have the same difficulty.  I don't know
of a good removal method.

If this is the only anodizing job you want to do I'd strongly advise
taking it to a professional anodizing shop.  Even the small amount of
dye and sealer I bought cost more than the minimum fee for most
anodizing
shops.

Lou Boyd
Fairborn Observatory

From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Anodizing Experiment
Date: Thu, 15 Oct 1998 02:08:37 GMT

On Wed, 14 Oct 1998 15:21:06 -0500, "Kurt Bjorn" <pyroware@flash.net>
wrote:

>I have been working on an IC engine project for over a year now, and am
>getting ready to experiment with anodizing.  One experiment so far has been
>interesting, to say the least.  Here is what happened...
>
>I prepared a test piece of 6061 T6 by drilling and tapping and reaming a few
>holes to check for dimensional change.  In a plastic cup, I set up a
>U-shaped lead anode to which I connected the negative end of a small power
>supply.

In anodizing the piece to be anodized would be connected to the anode
(positive end of a small power supply). I presume that your "u-shaped
lead anode" was actually the cathode in this fiasco. Note: Fiasco
refers to the unique method for melting plastic and "painting" a shop
bench not the final results.

> I filled it 1/2 way with demineralized water, then slowly added
>sulphuric acid.  To my horror, the cup began to melt!

Next time measure out your water in the form of ice cubes. Assume
density of one and weigh the ice. Pour the acid into the ice cubes and
you will end up with a solution that is pretty warm but you avoid
getting it almost to the boiling point.

> Here I am standing
>there like a doofus watching a hot cup of nearly concentrated acid deforming
>and melting like the witch in The Wizard of Oz.  "I'm melting.....
>melting...."  Sure enough the cup collapsed dumping a pint of sulphuric acid
>all over my bench and floor.  I escaped with a few droplets on my leg. WOW!
>Grabbed some baking soda and began spraying it all over the spill.  The
>baking soda hissed like mad and crystallized into some weird hard substance.
>WHAT A MESS.

The hard way to make sodium sulfate and/or sodium acid sulfate.

>Two hours and a lot of scrubbing had it cleaned up.  Back to square one.  It
>was the HEAT which melted the cup, so a new cup was immersed in an ice bath,
>and the acid added much more slowly.  I immersed the part and switched on
>the current.  Lotsa little bubbles.  I let it cook for maybe 15 minutes (too
>short) and rinsed in more demin water.  I tried to dye the piece with
>nigrosene black die, but the surface didn't take it at all, so i simply
>fixed it in a hot water bath.


>SUCCESS!  The anodizing is quite thin but definitely there.  I have another
>piece cooking at this moment, i plan on a 45 minute session.
>
>Here are some observations:  The piece started at .1874" thick and ended up
>.1870, loss of .0004.  The threaded holed anodized too and easily accepted
>4-40 screws with no difference between the unanodized piece.
>
>I plan on ordering a rather fancy power supply from an electronics house, 0
>to 30v and 0-5 Amps DC, can run in constant current or constant voltage mode
>so I can fine tune the current.  I plan on using the power supply for both
>anodizing and electroplating/electroforming.

When you get to electroplating get a copy of the Electroplater's
Handbook. For electroforming look into pulsed DC and (damn Alzheimer's
has struck) reverse pulse plating. What they do here is run the
current plating in one direction (plating) and then for a shorter
duration reverse the current (stripping). Without going into more than
anyone wants to know this smooths out the plate and gives a  more
dense plate (assuming it is done correctly). It tends to avoid
dendrites and bridging.

Look up Harvey Diehl in Chemical Abstracts if you have access to a
chemical library. He published a procedure for making silver crucibles
by electroforming silver on an iron crucible and then dissolved the
iron crucible with hydrochloric acid. Probably in the 60's or 70's.

>Anyone out there a genius on anodizing?  Can you help me with some hints or
>possibly links to non-industril anodizing information?  Good books to
>recommend for the home shop guy?

It can be done on a lab bench without much sophisticated equipment.
You probably won't get the quality of coating that you see from an
industrial source.

Run your keyboard over into sci.chem and ask for suggestions on books
on anodizing there. I'm sure you will get some suggestions there
probably from Uncle Al. I am retired and too far from a library to dig
up current information. As I recall it is more witchcraft than science
and that is not to say that the people doing anodizing weren't good
chemists.

I believe that a calcium salt is frequently added either during the
anodizing or during the fixing process. Don't try that in your
sulfuric acid as it will precipitate insoluble calcium sulfate.

>More to follow, hee hee this is fun.

Yes but do wear eye protection (good goggles) if you are splattering
H2S04 around the shop. If you can't get started on some literature
contact me by email and I will try to contact some of the guys that
haven't retired.

From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Electricity guys - HELP PLEASE!!
Date: Thu, 29 Oct 1998 11:19:18 GMT

On Tue, 27 Oct 1998 20:33:52 -0600, "Kurt Bjorn" <pyroware@flash.net>
wrote:

>I have been doing some anodizing lately, and am having problems.  I recently
>purchased a 30 amp DC power supply (regulated) for my efforts.  The setup
>consists of an electrolyte (sulphuric acid or Sodium Bisulphate) a lead
>cathode, and the aluminum anode.  Every article I've read on anodizing calls
>for a certain current per sq cm.  The resistance in the bath is 2 ohms.

When you pass a current through a solution there must be a chemical
reaction at the anode (oxidation) and another chemical reaction at the
cathode (reduction). No reaction no current. As you increase the
voltage in the circuit the current flow will be minimal until you
reach a potential where the oxidations and reductions can take place
and of course you must have a reaction at both electrodes. In some
cases the reactions at the electrodes may not necessarily be the ones
that you desire.

Over at your lead cathode you probably will notice bubbles when the
reduction gets going and this is hydrogen gas leaving your system you
describe. Non-believers can collect the gas and light a match.

At your anode aluminum metal will be oxidized to aluminum ions. This
takes care of the current carrying necessities. In electroplating the
business end of the system is almost always the cathode and the
reaction product (reduced metal) gets out of the way and also provides
a fresh surface for additional metal ions to snuggle up close to the
cathode and produce more deposit. The resistance doesn't change much
as long as you don't try to run the reaction too fast or too long.

In your anodization when those aluminum ions appear at the anode they
start building a surface layer of hydrated aluminum oxide. This oxide
layer does two things which tend to limit the current. 1) The oxide
layer is insulating so the internal resistance of the cell increases
and 2) the nature of the layer discourages diffusion so the electrode
has a problem doing its thing (oxidation). The aluminum ions collect
around the anode and form a hydrated aluminum oxide. In doing so they
produce hydrogen ions. The net result is a build up of plus charges at
the anode. Without the oxide layer (which inhibits diffusion) these
plus charges (either Al+3 or H+) would rather rapidly leave the
electrode surface for the bulk solution. The net result is that you
need to throw a whole bunch more volts at it to get something to
happen.

If you throw too many more volts at it you can get oxygen evolution at
the anode and this can pop the layer off. Murphy is ever present.

>I initially set up the circuit with a long piece of nichrome wire to act as
>a power resistor, thinking the amperage would shoot off the scale without
>it.  Other articles suggest a big rheostat, which I'm sure would work fine,
>I just don't have one.

You didn't say what type of power supply you had but it sounds like it
isn't adequate for what you are doing.

>Here is the problem:  I cannot get the necessary current to flow through the
>setup.  Even without the nichrome wire, a circuit which needs, say 800 mA is
>drawing only 100 or so.  The power supply is fine, when connected across the
>nichrome wire, it glows fiercly and can draw 10 or more amps.

As I understand what you are saying..... The piece you are trying to
anodize should have 0.8 amps flowing to form a decent anodized layer
but in fact with your power supply cranked up full blast you are only
getting 0.1 amps. Sounds like you need more volts or less surface
area.

If feasible try using a test panel substantially smaller. Perhaps with
one-tenth the surface area. (Don't forget that if it is a flat piece
of Al it has two sides). That was not meant to be insulting. There
probably isn't a electroplater alive that didn't make that mistake at
least once. Will your power supply handle this? If so then you need
more volts for whatever you are trying to do.

You have not said what kind of coat you are trying to make. For a
softcoat in sulfuric acid (0.2-0.7 mils) 24 volts may be enough for
8-15 amps per sq. ft. with the solution around 70 degrees F. For a
hard coat (1-3 mils) you may need to go to 50 volts or more to get
20-25 amps per sq. ft with a starting voltage of 20-30 volts and the
solution cold. In either case as the film increases in thickness more
voltage is required.

NOTE: This is not a constant voltage operation. The nature of the
beast is that as you build thickness in that insulating layer it is
going to take more voltage to drive the same number of amps through
the circuit. In other words to make a decent layer you may need to
stand there and crank up the power supply as the layer builds or as
someone suggested use a constant current power supply.

BTW to go from amps/sq ft to amps. sq cm dividing by 1000 will
probably be close enough. Actually 929 and a dribble.

>I would think with a 2 ohm resistance, there should be more current.
>
>If E=IR, then I = E/R, I = 15v/2 ohms = 7 Amps!!  Am I in outer space here?

No Murphy has not had a finger in Ohm's law.
The problem is that your resistance R is not just what you measure in
the bulk solution. To show mathematically what I was trying to explain
above.....

R = (bulk solution resistance) + (anode layer resistance) + (cathode
diffusion layer resistance) + (the minimal and constant resistance in
the wires)

Now the term concerning the cathode is essentially constant (in this
case) and small BUT your anode layer resistance can get huge as you
build up a layer of hydrated aluminum oxide. In fact if your anodizing
is any good the layer should become an insulator. No current.

>I tried a fresh car battery, too, with identical results.

12 volts I presume. I hope that you didn't get your power supply based
on the 6 to 12 volt recommendation of the pseudo chemist.

>Please electricity gurus, any light you can shed on this, suggestions, etc,
>would be MOST helpful.

It is a chemistry problem but.....

Try a smaller piece so the surface area is small enough so that your
power supply can supply the recommended amps per cm2. This will tell
you if your set up is OK. It may be that you are just trying to
anodize a larger area than your power supply can handle.

You didn't say whether you were trying to make a hard coat or a soft
coat. The conditions are different. Also don't forget that I*R also
produces heat and that you seal the anodized layer with hot water.

Perhaps the pseudo chemist will again suggest that I don't know what I
am talking about and give you better advice.

From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Electricity guys - HELP PLEASE!!
Date: Fri, 30 Oct 1998 04:50:25 GMT

On Thu, 29 Oct 1998 09:23:20 -0600, "Kurt Bjorn" <pyroware@flash.net>
wrote:

>Don, thank you for the VERY detailed reply.  You have increased my knowledge
>of anodizing 500%
>
>Don Wilkins wrote in message <36394073.459672@news.wcta.net>...
>
>>When you pass a current through a solution there must be a chemical
>>reaction at the anode (oxidation) and another chemical reaction at the
>>cathode (reduction). No reaction no current. As you increase the
>>voltage in the circuit the current flow will be minimal until you
>>reach a potential where the oxidations and reductions can take place
>>and of course you must have a reaction at both electrodes. In some
>>cases the reactions at the electrodes may not necessarily be the ones
>>that you desire.
>
>
>I can already see where this is going.  I made a typical beginner mistake
>when it came to tool purchase, in this case the tool being the power supply.
>The supply I purchased is a simple supply, 15v regulated, 30 amps maximum.
>Well, all the rated amperage in the world cannot help me if there is not
>sufficient voltage to drive the reaction.  What I SHOULD have purchased is a
>constant current, higher voltage DC supply.  Darn it!!

Don't trash that power supply yet. If you are doing such small parts
it may be OK.

I ran across a web page that may be of interest to you.

Try

http://www.warpig.com

No that isn't a hobby of mine. Go to the bottom of the page and you
will find a search dialog box. Type in "anodizing" (no quotes) and it
should take you to an article entitled "Anodizing at Home".

He is doing this at 12 volts in a fairly concentrated sulfuric acid
solution. He uses RIT dyes but I don't believe they are made for
anodizing.

There are two companies that I am aware of which specialize in dyes
for anodized aluminum. They are Clariant and US Specialty.

http://www.clairiant.com   They have a lot of dyes made specifically
for anodizing. Poke around the page until you see "search", click on
it and type in "anodizing". You get two hits (actually only one) which
lists some of their dyes, etc. I would either write or email and ask
for literature on their dyes for anodizing. In addition you might ask
if they have any literature on the anodizing process they recommend
for their dyes.


<stuff snipped>

>>If you throw too many more volts at it you can get oxygen evolution at
>>the anode and this can pop the layer off. Murphy is ever present.
>
>I saw this when I experimented with a high voltage DC supply... the reaction
>was vigorous but the surface was rough, flaked, and pitted.  I must admit at
>this point I was annoyed and simply cranked up the voltage without worrying
>about the finish.

Not an unusual occurrence. Done similar many times.

>>>Here is the problem: I cannot get the necessary current to flow
>>>through the setup.
>>
>>As I understand what you are saying..... The piece you are trying to
>>anodize should have 0.8 amps flowing to form a decent anodized layer but
>>in fact with your power supply cranked up full blast you are only
>>getting 0.1 amps. Sounds like you need more volts or less surface area.
>>
>>If feasible try using a test panel substantially smaller. Perhaps with
>>one-tenth the surface area. (Don't forget that if it is a flat piece
>>of Al it has two sides). That was not meant to be insulting. There
>>probably isn't a electroplater alive that didn't make that mistake at
>>least once. Will your power supply handle this? If so then you need
>>more volts for whatever you are trying to do.
>
>I am already using sample pieces the size of a postage stamp.  The power
>supply i am using doesn't seem to have the voltage necessary to really get
>the reaction going.  I have heard of guys anodizing with 12v car batteries
>and saltwater "rheostats"; they must be using a different electrolyte or
>something.   My aluminum is VERY clean, having been pickled in a solution
>specifically designed for removing all traces of oxides in preparation for
>TIG welding.

With that small of a piece you should be able to anodize. Don't rush
for a new power supply.

How about a name or better the composition of the pickling solution.
What may be OK for welding may not be so good for anodizing.

>>You have not said what kind of coat you are trying to make. For a
>>softcoat in sulfuric acid (0.2-0.7 mils) 24 volts may be enough for
>>8-15 amps per sq. ft. with the solution around 70 degrees F. For a
>>hard coat (1-3 mils) you may need to go to 50 volts or more to get
>>20-25 amps per sq. ft with a starting voltage of 20-30 volts and the
>>solution cold. In either case as the film increases in thickness more
>>voltage is required.
>
>A simple, repeatable soft-coating is what I seek, for now.  Temperature is
>one aspect I haven't monitored.  The electrolyte starts at room temperature,
>and heats gradually to perhaps 130 degrees f.  Does it need to be kept
>cooled, perhaps in an ice bath?

Soft coats are usually done around room temperature. I don't know if
130 F is enough to seal it. Once sealed you are not going to have much
luck with the dye. What is supposed to happen is the dye gets into the
coat and then gets sealed in.


>>R = (bulk solution resistance) + (anode layer resistance) + (cathode
>>diffusion layer resistance) + (the minimal and constant resistance in
>>the wires)
>
>
>Someone else pointed out the folly of attempting to measure resistance of a
>cell.  It is a dynamic chemical reaction which will vary resistance wildly
>once it begins to "cook".

<stuff snipped>

>I don't know who the pseudo-chemist is, perhaps it is me!  ;-)

If it had been you I wouldn't have written anything.

I also ran across a note by Robert Allen at Southern Industrial
Chemicals no address but  1-800-394-9770 looks promising if it is
still valid.

The note said that you could ask for Allen or Wayne Chandler. Now the
later name is followed by (the Pres. of SIC)  I presume that means
rather high up on the food chain there.
He says that they have an anodizing handbook and they do sell various
chemicals which look appropriate for anodizing and provide technical
support (I presume for their products).

Also a note by Lee Branch at Albright Wilson. Apparently in Richmond
VA. You might try yellow pages ofr an 800 #. He apparently has a
Technical Bulletin. They have a Web page but I couldn't find an email
address.

Don't rush now. You could end up with a collection of power supplies
to sit on the shelf. Better to become more acquainted with the process
and then get the stuff you need.

I presume that you will follow some of these leads. You should be able
to get enough to get started. Let me know if I can be of help.
Unfortunately where I live now I don't have access to a technical
library.

From: REMOVE_THISdwilkins@means.net (Don Wilkins)
Newsgroups: rec.crafts.metalworking
Subject: Re: Electricity guys - HELP PLEASE!!
Date: Fri, 30 Oct 1998 13:04:24 GMT

On 29 Oct 1998 22:48:42 -0500, dnichols@d-and-d.com (DoN. Nichols)
wrote:

>In article <71a1be$ljl$1@excalibur.flash.net>,
>Kurt Bjorn <pyroware@flash.net> wrote:
>>Don, thank you for the VERY detailed reply.  You have increased my knowledge
>>of anodizing 500%
>
>>Don Wilkins wrote in message <36394073.459672@news.wcta.net>...
>
>	[ ... ]
>
>>>If feasible try using a test panel substantially smaller. Perhaps with
>>>one-tenth the surface area. (Don't forget that if it is a flat piece
>
>	[ ... ]
>
>>I am already using sample pieces the size of a postage stamp.  The power
>>supply i am using doesn't seem to have the voltage necessary to really get
>>the reaction going.
>
>	A thought occurs to me.  How are you connecting to the aluminum
>samples?  (That may have been somewhere back in the thread, but I don't know
>at this point.)

It is a good thought and I would like to see the answer. In general
when you apply a voltage under these circumstances the reactions start
with the easiest to oxidize going first. If you increase the voltage
the current will increase up to the limit of the carrying capacity of
that reaction. Additional voltage increases will start looking for
something else to oxidize. If nothing is found then one has reached
the limiting current. In his case it should go to zero as the coat
builds the insulating layer.

This description may make some electrochemists uncomfortable but it is
reasonable accurate. The description of course was for the anode. Over
at the cathode he is making hydrogen and that will go until his acid
concentration is too low.

He said he was getting 0.1 amps on a piece the size of a postage
stamp(USA I presume) which is about .875 X 1 inch. That gives him
approximately 1.75 sq inches to anodize. So 0.1 amps on 1.75 sq inches
comes out to about 8 amps per square foot unless Alzheimers has had a
serious effect on my math (a possibility) and that should be enough to
do some anodizing.

Now since the solution is getting hot there must be current flowing.
If the piece were reduced in size by 50% it would put him right in the
current density range for softcoat anodizing.

I would 1) mask off one side, or 2) trim the piece, or 3) get some
aluminum wire for test purposes.

My choice would be the latter. He can vary the current density by the
length of wire dipped in the solution, the material is cheap, there
are no connectors in the solution, and it is easy to calculate current
density. I can go to the local scrap yard and get a few feet of
aluminum wire for $1. If the guy is in a good mood I would get it
free.

>	If it is not with aluminum wire, you will have other reactions going
>at the wire itself, and this may be complicating things for you.  (Let's
>see -- a alligator clip has cadnium plating over steel, with steel springs
>and rivits, and possibly copper wire, and possibly solder ...
>
>	You *really* need all parts in the solution at the anode to be
>aluminum -- no steel, and most other metals are bad choices too.  Perhaps
>titanium will work, however. :-)

Good point. Titanium can also be anodized. Anything that is anodized
will become insulated and be OK but stuff that goes into solution like
alligator clips will just disappear and perhaps screw up the solution.


I think he should get some aluminum wire and play with the system to
learn what is going on before getting another power supply.

From: "Kurt Bjorn" <pyroware@flash.net>
Newsgroups: rec.crafts.metalworking
Subject: Re: Electricity guys - More observations/summary
Date: Fri, 30 Oct 1998 12:34:34 -0600

This has been, for me, the most helpful thread I have started on RCM... too
many guys to name have contributed valuable advice.  If I did not reply
personally to your posting, accept my apologies and thanks, I have read and
re-read them all.

I will summarize what has happened with some new parameters and some
suggestions by the guys.

The supply I have (thank goodness I didn't buy another) will work fine.  My
problem resided in the strength of the electrolytes I has using, as well as
the method of contact I was making with the work piece.

First, the electrolytes:  I have tried sodium bisulphate, sulphuric acid,
and TSP.  All will anodize.  After many test pieces, the sulphuric acid is
the winner.  This contradicts a posting I made before about sodium
bisulphate being superior.  In all cases my electrolyte was too weak.  For
sodium bisulphate, I was using a 20% solution, ie 200 grams dissolved in 800
mL water for 1000 gram electrolyte.  While this particular electrolyte was
in use yesterday, on a whim I began to feed in some solid sodium bisulphate
and watched the current flow dramatically jump.  I kept spooning it in (I
have a magnetic stirrer) it kept dissolving, and the current kept
increasing.  I was FINALLY able to achieve specified current on less then
18v, my supply max.  In fact, 10 or 11 v was adequate.

I also found that stock battery acid, mixed 50/50, produced similar results,
plenty of available current.

The articles I had read called for ~150 mA Sq/inch.  By increasing that to
~250, the anodizing porosity and depth increased to the point that some
aniline dyes I had on hand worked like a champ, with the coloring nearly
opaque, no underlying metallic sheen.  This also called for times 2 or 3 X
that of "book", maybe 45 minutes rather than 15.

I had been using Al MIG wire to suspend the pieces, but the contact was
poor, so for real work, I will use thick grounding wire attached to
available screw holes with aluminum hardware.  The piece will be rotated by
a DC gear motor at maybe 3 rpm.  The cathode will be a lead strip with 360
degree radial coverage.

Thanks again for all of the helpful suggestions.  When (and if) I get better
at this, I'll write an article and post it on the WWW somewhere.