"Andy Dingley" wrote in message
...
On 16 Jul, 09:24, wrote:

I want to do some anodising, and I am trying to locate a source of
sulphuric acid.

Liquid drain cleaner. The acidic ones for unblocking drains are conc.
(96%) sulphuric. Just check that it's not either alkaline / basic
sodium hydroxide, and that it's not a limescale shifter based on
sulphamic or formic acids. Mine (for electroplating) costs me about
£6 / litre and is available from the local hardware shop. It's not
hard to find.

Aluminium is a faff to anodise and you might prefer to start with
titanium, which is _far_ easier. Use Pepsi as an electrolyte and a
variac (with rectification), or else a variable bench PSU that goes to
fairly high output voltages.

A bit vague on the details as it was some years ago that I used to maintain
the baths on an anodising plant, but you may find that it is the current
that defeats you. You have to have the requisite amount of amps per square
metre of surface to be anodised. At home, I could only manage pieces up to
a few inches with the battery chargers I had to hand. In our baths we had
aluminium girder bus bars that typically took 1500 amp at 12-15 volt. Quite
spectacular when one day I happened to drop an aluminium step ladder across
them!

Also, you might note that the new coating has to be sealed - typically by
boiling in water to make the oxide swell and become less porous. It is this
swelling that seals in the various colours you see in saucepan lids for
example - the dye being added to the sealing water bath. (We also sealed
our printing plates with a chemical solution, but it was nasty stuff, so
boiling water is your best bet. That said, I did some of my motorcycle
parts boiling in candle wax, and they came out quite nice too.) The water
has to be very clean (distilled or deionised) or the coating gets
stained/smeared.

Another thing you should note, is that the colour you get depends on the
alloy. Most 'aluminium' is actually an alloy with magnesium 'Magalloy' (has
a pinkish/bluish tinge), but there is an enormous range of alloys for
different applications. These in turn have different sized crystals
depending on how they were made and heat treated or cast. The anodising
current picks out all the imperfections and crystal boundaries, and the
different alloying metals make oxides of varying colours. Result is, you
never know quite what you are going to get. Sometimes you get a lovely
pattern of big crystals: sometimes you get black (my bike bits came out a
nice stony green/black).

Also, the existing oxide on the metal is best removed first - which we did
by dipping in well agitated caustic soda solution.

Thus there are lots of ways for this to go 'wrong', but all of them produce
interesting results. Just perhaps not what you are after!

S