I'm in the last stages of building Dick Stephens' centering microscope. The
aluminium parts need to be anodised to stop reflections. Whilst I could get
this done professionally I'm inclined to give it a try myself - the
instructions on various web sites seem simple enough.
Has anyone done this? Any pitfalls? In particular there are obviously bits
that one would prefer not to anodize - what would you use to cover them to
stop reaction? My thought is to use paraffin wax deposited from solution -
just really an oily layer.
Any advice gratefully received
Will you be using a kit?
Paraffin wax, hmm - it should withstand the etch, desmut, anodise and dye
stages if the anodise isn't too hot - the seal stage might be a problem
though, as the water might have some dye in it and the temperature will be
high, might give some faint cosmetic stains. Worth a try though I'd say. If
you use a hot water seal and a high melting point wax I'd guess it would
Do you mean not colour? That's trickier, not to get stains on the uncoloured
anodised parts. An unsealed anodised surface is highly absorbent and I doubt
you would successfully get the wax off. Latex might do it - one chap I know
used cow gum, easy to remove, but I can't remember exactly what for and what
parts of the process it went through.
In rough order of importance:
 Clean thoroughly. You should not touch the cleaned parts with anything at
all after cleaning - not even cotton gloves - so attach the wires before the
final cleaning and handle only by the wires - you may need a frame.
Considerably more than half the price charged for professional anodising is
actually for cleaning and handling - the importance of cleaning is often
 Run through the entire process with some scrap bits of the same alloy(s)
you will be anodising.
 Use aluminium (difficult to get a good connection) or titanium for the
frames and the wire to attach to the current - not copper! Titanium is used
professionally as it can be reused more easily - aluminium frames get
anodised and then you can't attach the current. Also titanium retains it's
springiness, by which the parts are held in place on the frame.
 Use the proper dye - there used to be a chap on uk ebay who sold it, but
he seems to have gone, however there is a chap on german ebay, Seller:
electronic-thingks see Item number: 6056354483 - he also sells titanium
wire. I haven't dealt with him, but his prices seem reasonable. Don't pay
germans by bank transfer though, it costs a lot.
Using the proper dye is especially important with black. If you need to
deepen the black after you have gotten it as dark as you can, dye again (or
dye first is better) with yellow.
 A warm seal gives the best surface - deionised water at 70 centigrade for
30-40 minutes. However this may leach out the dye, and if so a steam seal is
a good compromise. Steam for 10-20 minutes after dyeing to seal the holes. A
domestic steamer will do for small parts, but it will probably stain - don't
use the missus's best one...
A large professional system might go like this:
1) inspection, mechanical cleaning
2) load in frames
2b) degrease recovery
4) etchant recovery
8) desmut recovery
12) anodising recovery
16) dye recovery
20) warm rinse
21) air dry
22) visual inspection, tests for the thickness and porosity of the layer.
Some or all of the rinses are done in deionised water. The recovery stages
are partly to conserve the reagents, but also to minimise contamination of
the expensive rinse water.
There are five or six main processes after loading in frames - degrease,
etch, desmut, anodise, dye and seal. Degreasing is used partly to keep the
etch clean - etches will usually attack grease. Degreasing is not done very
For the home anodiser, only etch, anodise, (dye), and seal are essential.
Desmut is only needed on some alloys. You can do a combined etch and desmut
using an acid etch.
A brief description of the process may help - the surface is cleaned, then
etched. Desmut gets rid of any non-aluminium metals from the alloy on the
surface which might interfere, and leaves a mostly-pure aluminium surface.
Anodising grows a layer of aluminium oxide - this is slightly smaller than
the underlying aluminium and fractures into adherent flakes which look like
old threepenny bits under a microscope, with gaps between. The threepenny
bits themselves are also porous.
As you may imagine, this surface will pick up dirt, grease from fingers, and
so on like almost nothing else. It is highly absorbent.
Dye gets into the gaps and into the pores, then the dye rinses take some of
the dye back, mostly from the gaps. The dye should stick to the oxide, but
it doesn't do that terribly well.
In sealing the oxide is then partly converted to aluminium hydroxide*, which
is larger than the underlying aluminium - the threepenny bits swell up and
the gaps close, and the pores close too. This is now the impervious surface
of an anodised part.
BTW this is all for type III sulphuric acid anodising, the most common type
- there are other types but they are not really do-able at home.
Not for the anodising - I have access to chemicals through work so its no
I am building the microscope from the kit - mainly to get the lenses,
graticule and eyepiece - the rest is just a soft MT2 arbor a couple of bits
of aluminium rod and some tiny screws.
Many thanks for all the information. I guess I'll give it a try and see
what happens. Its really only a matter of getting the insides of the tubes
black to avoid reflection - everything else is cosmetic.