Common Defects: Color Non-Uniformity

Streaks and spots that may be partially colored can sometimes be found on individual parts and sometimes they can relate to the parts position on a load.

Non-Uniform Part

The color of individual parts may be mottled or have streaks. This is likely due to inadequate rinsing which may be exacerbated by high aluminum content in the anodize acid. It may be time to decant the anodize bath. Improved rinsing practices may include warm water and nitric conditioning. Foreign matter in the dye tank (oil, mold, etc.) can be the cause of spots or streaks that are partially colored and maybe even white looking. Inadequate cleaning can also result in an anodized coating that is partially masked and poor to pick up dye.

Non-Uniform Load

The color of parts on a load may not match up. Most often this is the result of coating thickness variations within the load. Ensure that the parts are well distributed in the anodize tank and that the anodizing is not done too quickly. Better to take 45 minutes to reach 0.7 mil rather than 25 minutes. Another cause of this problem may be too short of a dye time. The lower racked parts are immersed a few seconds shorter than the upper, and this may play a role if the dye time is only 30 seconds in all.

E-Color Parts

Mottled e-color may be due to insufficient dwell time before initiation of the electrical program. Lighter color in deep recesses is normal, but the variation can be minimized by adjusting the chemistry and/or electrical program. Parts should be racked so that they do not shield one another from the electrodes and they should be well distributed along the length/depth of the tank. Accelerated anodizing can cause coating softness near the contacts and corners, which can ultimately result in color variation.

E-Color Load

The entire perimeter of a load may be darker or sometimes lighter in color. If this is the case, and you are satisfied that the anodize process is reasonable, then look to the electrical program for coloring. The voltage may need to be reduced a little. If modulated, you may need to cut back on the bias. Make sure that the thysistors are in good working order.

To our best knowledge, the information and recommendations contained herein are accurate and reliable. However, this information and our recommendations are furnished without warranty, representation, inducement or license of any kind, including, but not limited to the implied warranties of merchantability and fitness for a particular use or purpose. Customers are encouraged to conduct their own tests and to read the product labels carefully before using them. Furthermore, the customer assumes sole liability for any patent infringement that occurs by reason of their following our recommendations or using the information given.


This area is reserved for offline development of new content.