A good anodised coating thickness

Coating thickness will be built up after 40 minutes at the
calculated current density. Keep a running check on the current reading as this will tend to vary during the process.
Too low a current setting will result in a surface that will have difficulty
absorbing the colour dye.
Too high a current setting will result in overheating the tank solution and a porous finish which will leach out the dye during fixing.
A good anodised surface will have a slightly milky appearance when ready for fixing; or colour dyed and fixed.
Copper , brass. or iron will contaminate the tank and degrade the process.
Use only lead or aluminium contact strips. I use wooden clothes pegs to set my workpiece height in the tank.
Few, if any, parts you make will be made from pure aluminium. Most will be made from aluminium alloys which contain varying proportions of copper, manganese, silicon, and sometimes, other elements in the mix. These alloys have an effect on the ultimate colour shade obtainable with a given dye and process. If colour shade repeatability is required, the same alloy, process times, and temperatures must be carefully duplicated. Previously anodised parts must first be strip-cleaned in a strong Akali to remove all traces of prior anodising oxides.