Avoiding Anodizing Headaches

As in any process, there are always limits and special conditions that can become a nightmare if you do not take some precaution to avoid it. Our aim is to help you to prevent complications and avoid additional costs and problems.


Ultraspec offers different combination of processes using proper masking material, techniques and process sequence to meet complex engineering requirements and needs

Hollow parts or parts with a hollow section

Since the parts are to be mounted on stands to be submerged in different solutions, a part with an hollow section, opened or closed on one side is inherently risky. It may form an air pocket into the hole that will prevent the treatment in this area. During the anodizing process, gases are released and potentially accumulate into cavities. Our qualified personnel are familiar with these constraints and will position parts so as to prevent this phenomenon. However, when parts have complex geometries, sometime we can not position them without risk. Additional costs may be associated with this problem and unfortunately in some cases, air pockets are unavoidable.

Welded part / alloy 5356

A weld on a piece will alter the microstructure of the aluminum alloy used initially. Tempering or annealing will be permanently affected by the intense heat input during welding. The filler alloy will also be merged with the original one and will change its properties. Result and consequence for anodizing: a different color will certainly be seen. However, 5356 is recommended as filler alloy (5356 rod for the TIG process, for example) and it will in many cases minimize the visual effect of the weld. Keep in mind, welds will be darker than the alloy of the assembly from lightly grayer to dark charcoal. Ask us for more detail!

Contact Point and mounting mark

As your parts must be mounted on stands to be submerged in different solutions, and for anodizing, an electrical current will flow through your parts, there is no treatment without contact point and mounting mark. This is as been said, we make sure to minimize the visual impact and functionality of the latter and require your cooperation in order to properly identify the desired location in critical cases.

Finish defect prior anodizing

Anodizing will not hide surface defects. Unfortunately, anodizing tends to amplifiy the minor defects (holes and scratches). However, an aggressive etch could in some cases blend the surface finish but never eliminate it.

Extrusion lines

Extrusion lines are considered as a surface defect and will not be totally hidden by anodizing. They are caused by the wear of extrusion tools and unfortunately they will not disappear during processes.

Water stain

Bare aluminum oxidizes naturally in the free air and the presence of water or coolant will cause stains which are very likely to appear even after the treatments. Protect and clean your aluminum before and after your operations.

Cast aluminum alloy

Some cast alloy are not possible to anodize. The presence of silica and other elements can be a real danger to your parts during anodizing. Some elements will be eroded and increase the porosity of your parts. Some other will cause electro erosion and will burn edges and some critical area of your parts. Please select proper alloy from your supplier before spending time and money or call us.

Mix of aluminum alloys

To perform effectively and safely your parts, we need to know the aluminum alloy used to make them. As different alloys have different conductivity resistances and widely different ability to be anodized, a mix of alloy may cause damages on your parts. Burning phenomena of the anodic layer and electro erosion could take place without the possibility of being detected early enough to save the lot. Please de not mix alloy without identification and lets us know.


When the parts are assembled by welding or bolting, gap created between the sides, is a major risk of infiltration by chemical solution. During preprocessing, solution of caustic soda will fill gap and then be released during sealing at a higher temperature. This corrosive solution will attack the anodized coating of your parts, and is a risk to your staff like ours and also an environmental risk. If your assembly can be disassembled, do so. This is the best solution for you, your parts and your safety. If your assemblies are welded, even if the welds are all around, allow drainage holes big enough to allow quick drainage capability, function of the cavities size and limit face over face as much as possible. Also, removed all steel anchor part as screw, bolts, nuts, washer, ring, insert, pin… Steel is not compatible with our chemical solutions.

Folded or rolled edge

Same problematic than for assemblies, see above. There is a risk of infiltration by chemical solution.

Sharp edges and square corners

Anodizing is an electrochemical process and unfortunately there are side effects. Electromagnetic field on the edges has distortion and the highly organized nature of the anodic layer formation makes the process incompatible with sharp edges and square corners. Round edges and corner is possible is the best solution.

Finish dimension / tolerance

As explained in the various pages on the anodizing process, especially for hard anodizing, changes in dimensions must be considered in the design of your parts. As example, a machined bore with 0002'' of type III anodizing, will have its diamater reduce by 0.002'' (50% penetration per side). In the case of threads, the increase of 0.001''perpendicular to each side of each fillet will have an even more significant impact. Masking is a solution if hard anodizing is not required all over. Plan ahead and contact us for more information.


Porosity is a defect, a part made from a porous alloy to be anodized will show major defects after treatment. Anodizing does not hide anything as plating or paint.

Thin part

Part with thin section and sharp edges and will not be easy to anodize. Field effect and heat dissipation will be a challenge and will drive an uninformed coating speed rate. Some area will be gradually isolate during the process and some other area will become very conductive compared to the rest of the parts. This phenomenon will drive the process into a dangerous zone and can quickly erode a thin part. To prevent problem in some case, the current density will be low to minimize the risk. The cost will be affected and the risk of losing good parts is present.

Plastic film

A plastic film covering a surface of aluminum can be a good solution to protect surfaces from scratches before treatment. However, it provides a cost for the remove it. Also, it is possible that plastic substances, invisible over parts initially, contaminate the surface and become visible after treatment. Especially after dyeing. Ultraspec will not be held responsible for this phenomenon. Asked to make a sample before processing too many parts.

Painting, printing, ink, glue, silicone and grease on the aluminum surface

Those products represent real problems for finishing of your parts. They must be removed with a solvent or acetone prior to anodizing. Please remove it before shipping. Otherwise, we will remove it ourselves and additional charges will apply.

Coolant, machine tools

You probably use machine tools coolant, cutting fluid and lubricant to machine your parts. Make sure of the quality of those liquids. A liquid too old and contaminated can contain algae and bacteria and can stain your pieces even if it is not visible before anodizing. Also, wipe out your parts and do not let your part too long partially covered with these fluids. It is easier to prevent than to try to save your finished parts and it’s certainly less expensive.

Our Techniques

Surface finish


Ultraspec offers different aluminum brushing services


The anodized layer is porous and can be colored.