Tony,
Just one comment.
Sandoz AG is now Clariant AG and they are very good not only in metallic golds
and bronzes, but also in many other colors. I don't now if they are still
producing Sanodal Black MW, one of the best dyestuffs for aluminium.
BR,
Ricardo
p.s.: I worked there 21 years as the R&D manager for the Chemical Division in
Brazil
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Data: Fri, 25 Apr 2008 12:34:40 +0100
Assunto: Anodising aluminium
> Hi all,
> Following on from Chris' recommendations and for anyone new to the SML
> here is a repeat of my instructions for simple home anodising of
> aluminium. It really is a simple process which turns a dull and lifeless
> metal into jewel-like material. Provided that good ventilation and basic
> safety procedures are employed it is a very safe procedure which
> produced hundreds of beautiful items made by students over the years
> with no ill effects.
>
> Tony Moss
>
> **************************************
>
> Anodising Aluminium in the Home Workshop
>
> 1. You will need a large acid-proof plastic container. Any polyethylene
> bucket or tank will do into which your workpiece will fit with a three
> inch gap all round. Alternatively I made purpose built tanks out of
> marine plywood covered with a liquid-proof layer of glass-fibre resin
> and surfacing tissue. After years of use these tanks are still in good
> working order.
>
> Just one very large tank will serve but of course this will need a lot
> of electrolyte.
>
> 2. Work outdoors or have good ventilation as the fine bubbles of gas
> which rise to the surface produce an weak acidic mist which is barely
> detectable - and then one day you discover you have lost your sense of
> smell! N.B. It will return eventually but better not to risk it.
>
> 3. You can anodise with low voltage AC or DC but if you use AC the
> `Cathode´ mentioned below MUST be of lead.
>
> 4 The cathode (negative connection) can be formed from a sheet of
> aluminium bent to fit around the interior walls of your tank as a loose
> `liner´. Leave a projection tab to bend over the edge of the tank with a
> terminal to which the negative wire is connected if you are using DC .
> If your power supply is AC then the cathode must be sheet lead.
>
> 5. Part-fill the tank with electrolye made by adding one part of
> concentrated sulphuric acid to nine parts of water. Wearing goggles and
> rubber gloves pour the acid SLOWLY down the side of the tank into the
> water. NOT the other way around. Pause if too much heat is generated.
>
> 6. Experiment with a piece of aluminium plate about 3" square to get the
> idea. Drill a hole in one corner and attach a pure aluminium wire by
> clinching with pliers to ensure a sound contact. 1/16" aluminium gas
> welding rods are perfect for this job.
>
> If contact with the wire is loose then the anodic film may form in the
> joint and this will stop the process. Design items to allow appropriate
> wire attachment - leave a cut-off tab or drill a hole in the base into
> which a filed taper can be `wrung/seized´ tightly.
>
> Hollow items can be held on an expanding zig-zag made to spring open
> into the inside. etc. etc.
>
> 7. Holding the object by the wire dip it into a strong solution of
> caustic soda (Sodium Hydroxide (NaOH) for a few seconds until it fizzes
> to remove natural oxides and grease. Rinse in clean water. Eye and skin
> protection are vital here so goggles & rubber gloves are recommended.
>
> 8. Suspend in the anodising tank supported from some kind of busbar. I
> use a square brass bar over the tank drilled at intervals with screws to
> clamp the wire into the holes and ensure a good contact.
>
> 9. Connect the positive lead of your power supply to the workpiece via
> the busbar and the negative lead to the Cathode lining of the tank.
>
> 10. Set the voltage to about 16v and in a few minutes fine bubbles of
> oxygen should rise from the workpiece. The oxygen produced by the
> electrolysis of the water in the electrolyte combines with the aluminium
> at the surface to produce crystal clear aluminium oxide (grindstones are
> made from it!).
>
> The oxide is produced is microscopic `tubes´ rising from the surface
> rather like a honeycomb. Electrical contact is maintained through the
> tubes and new oxide continues to form at the base thickening the film.
>
> After about 20/30 minutes you can switch off the current, remove and
> rinse in CLEAN water. The aluminium will have a whitish coating but DO
> NOT TOUCH IT or you finger prints will be captured for ever!
>
> If the object is now immersed in a cool dye solution - there are special
> dyes made for this but most household dyes work fairly well - the dye
> molecules will fill the fine glassy tubes to colour the item. Simply
> boiling in clean water for a few minutes will then cause the outer ends
> of the tubes to swell and seal off leaving you with a brightly coloured
> object which has a soft velvety feel and is impervious to general wear
> and weather.
>
> To get metallic golds and bronzes you will have to enquire of companies
> such as SANDOZ who may part with samples. They usually supply in
> expensive 1kg tubs which contain enough for 1000 years of home use.
>
> Voltage and Current
>
> Very small items such as rings and jewellery need a low voltage for a
> long time whereas larger items need a higher voltage.
>
> I have a GIF of a voltage/current/time graph derived from experiment
> which you can request when you get started but by setting 16 volts and
> allowing the current to take care of itself will be a good beginning
> from which to build up your own experience.
>
> Multi-colour anodising, photo-printing or writing on the anodic film
> with felt tip pens etc. are all areasin which I achieved good results
> and are there for you to experiment.
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