Anodising guide - 4. Anodising on your own

Now we come to the practical part, where we show you how to anodise and color aluminum quite simple. The results are impressive and are - if you take care - at least as good as in industry.

Because of the sometimes harsh chemicals, gases and vapors, you should perform all steps in a ventilated and insensitive room.

4.1  What can be anodised?

How well a piece can be anodised depends mainly on the used alloy. Pure aluminum is the best, but due to its softness is rarely used as material. The most common alloy for anodizing is AlMgSi0,5. Aluminum-silicon alloys with high silicon content are known for their very good castability and often also build good anodized layers - but these have a dark discoloration and are therefore not suitable for bright colors. A list of the most common aluminum alloys and their anodising and staining qualities can be found in our download area.
In principle: the purer the aluminum is present in the alloy, the better it can be anodized - and unfortunately the more worse it is for machining processes (drilling, milling). The distinction of the various alloys is difficult for the layman, but here are some hints:

• AlSi casting alloys mostly are dull and gray, while e.g. AlMgSi0,5 shines bright silvery on the cut surface
• How the part was formed? Casted parts are often highly alloyed with silicon because of their good castability. Extrusion/die casting parts mostly can be anodised very well.
• Today almost all rod sections are produced in the extrusion/die casting process.
• If in doubt, ask your manufacturer/dealer for a data sheet.

Furthermore, the surface of the workpiece plays an important role. When you cast parts, for example, you often get rough, porous, and sometimes cracked surfaces. By appropriate mechanical and chemical treatment such defects at least can be mitigated.
May be your profiles could be already anodised - please verify this before. An existing anodisation has to be removed by etching or mechanically before re-anodising!

In any case, with any new alloy you should do a trial with a piece of scrap!

Important:
During anodizing the workpiece becomes slightly larger due to the layer formation. Depending on the thickness produced 0.005 to 0.03mm are possible. Therefore in case of perfectly fitting parts this growth must be included. Threads, however, are not critical because of the relatively large backlash.

4.2  What do I need?

The necessary chemicals and materials should be available anywhere at a fair price. If you have problems in obtaining: all chemicals you need to anodizing you get in the pharmacy (of course some things are more expensive there). Below you find a list of quantities for first attempts:

• Sulfuric acid (H2SO4, specific weight 1,15 g/cm³, corresponding to 15-20% sulfuric acid)
  Quantity: depending on the size of the aluminum pieces - for the first steps in the range of 1-5 liters. Sulfuric acid for lead acid batteries is 37% sulfuric acid and is easily available and cheap. By dilution with distilled Water in a ratio of 1:1 you can adjust the desired concentration easily.
• Sodium hydroxide
  Sodium hydroxide (NaOH, caustic soda) is available in drug stores, pharmacies, and sometimes in hardware stores (drain cleaner). Quantity: calm more than 500g, it's cheap.
• Distilled water (H2O dest.)
  Quantity: 5 liters (canister)
  Distilled water you get very cheap in many grocery stores and hardware stores. Sometimes there is also the name demineralized water on the cans. This is practical the same and sufficient for our purposes.
• Dyes
  Best results you get with special anodisung dyes, of course. You can get these cheap and also in small quantities in our store. Since these colors stain very intensively, you need only small amounts (depending on color starting from 10 grams). These dyes have high light fastness and are therefore ideal for coloring objects outdoors (vehicle accessories, models, etc.). Other options such as textile dyes only work in individual cases, but have much less light-fasteness and are significantly less productive (and not cheaper). The results are not comparable with special anodising dyes.
• DC power supply with current control
• Plate/sheet made of lead or aluminum (about 10cm * 20cm)
  Lead sheets can be obtained for example from recycling companies or roofers, since it is used for roofing. Aluminum sheets you should purchase anywhere. Make sure that the sheet is not anodized.
• A thin wire/bar of aluminium or (better) of titanium
  for fixing your pieces in the anodising bath and for electrical connection.
• Correspondingly large plastic or glass vessels for anodising and dyeing bath and a heat resistant container for sealing.
• Possibly a pH meter and a hydrometer to determine the acid concentration and H3O+ concentration. Doing this you can achieve better results in film thickness and color quality.