An anodizing order usually starts with a colour and a part, and that is where the problems begin. The coating is an oxide layer grown from the aluminium itself, so the alloy, the temper, the surface before processing and the class of coating all change the result. Two parts machined to the same drawing can

A machined aluminium part measures perfectly, goes for anodizing, and comes back unable to accept its mating component. Nothing went wrong: the coating grew into and out of the surface, and the drawing did not account for it. Coating growth is one of the few finishing effects that is entirely predictable, which makes it one

Plating enquiries usually arrive as a metal name: nickel, chrome, zinc, tin. That is the wrong starting point. An electroplating system has to satisfy the requirement that matters, whether that is corrosion protection, wear resistance, electrical conductivity, solderability or appearance, and the same metal behaves very differently depending on thickness, substrate and the layer beneath

Aluminium is a common substrate for powder coating and a more delicate one than it first appears. The surface carries a natural oxide layer that forms within minutes of cleaning, it conducts heat far better than steel so thin sections heat and cool quickly, and it is soft enough that handling before coating leaves marks

A powder-coated part that will not assemble is a familiar problem, and it is always the same two causes: the film closed a clearance that was dimensioned without it, or a thread was coated when it should have been protected. Unlike anodizing, powder coating builds a film on top of the surface rather than growing

Both coatings are used to make a metal surface harder and more corrosion resistant, both build thickness on the part, and both are commonly specified on hydraulic rods, molds, wear plates and precision shafts. The differences that decide between them appear under load and in the geometry: one deposits by electrical current and therefore builds

Plating aluminium is a routine industrial process and a frequent source of failures, for the same reason in both cases: the metal carries an oxide layer that reforms the moment it is cleaned. Depositing a coating onto that layer produces a part that looks correct and blisters in service. The route that solves it, zincate

Powder coating is the cheapest way to give a metal part a durable, uniform finish, and the fastest way to lose a batch if the specification says only "black". The coating is applied dry and cured into a film, so its appearance and performance depend on the chemistry, the film thickness, the texture and the

Passivation is the least visible finishing operation and one of the few that a customer's quality system will ask for by name. It is also widely misunderstood: it does not add a coating, it does not change dimensions, and it cannot repair a part machined from the wrong alloy or left contaminated by an earlier

A welded stainless assembly that rusts along its seams is one of the most common and most avoidable failures in fabrication. The weld has changed the metal at the joint: heat has burned away the protective oxide, chromium has been drawn into the scale, and the surface that remains is chemically different from the parent