8 things you should ask your anodizer about

In my 25 years as a consultant in the anodizing industry, I realized that about 70 % of my consulting clients were not anodizers but the people who had to “deal with” anodizers. Perhaps you have had also frustrating experience ordering anodized parts and not receive what you wanted?

You might think that your anodizer was just not good at their job. Or that anodizers will always try to keep their costs as low as possible and thereby sacrificing the quality of your aluminum product. But that does not do the problem justice. In my experience, the main reason for errors and frustrations is ineffective communication. Yip, just like in any relationship, the relation to your anodizer will improve tremendously by learning how to communicate better.

8 important things to agree on with your anodizer

To make your next phone call with your anodizer much more successful, here is a checklist with all the aspects of the anodizing process you should talk about.

  1. Agree on the properties and quality of the anodizing results. 
  1. Choose the right alloy to achieve the properties you want. 
  1. Identify the microstructure of your different aluminum parts as this will affect the surface look. 
  1. Agree on handling and racking of the aluminum parts as part of the preparation. 
  1. Decide together on the right pretreatments for the specific parts of your aluminum product. 
  1. Set specifications for the anodizing process as these parameters affect the properties. 
  1. Choose the most environmentally friendly sealing 
  1. Agree on quality control tests that fit the properties of your anodized product. 

This checklist is a good start to improve the communication with your anodizer and to receive the correct anodized parts. If you would like step up your game even more and become more confident in asking the right questions, join my new live online training: “Working with your anodizing supplier.”  

Working with your anodizer - course overview graph

The course consists of four workshops, each treating an independent subject. You can also attend single workshop days. This interactive live online event is held on Zoom in 4 x 2,5 hours sessions. We will record the presentation and make them available to you after the workshop. The dates of our next courses are:


WORKSHOP SERIES IN APRIL: 7, 14, 21, and 28 April 2021 (03.00 - 5.30 PM CEST)  

WORKSHOP SERIES IN MAY: 5, 12, 19, and 26 May 2021 (03.00 - 5.30 PM CEST) 

Looking forward to seeing you at AnodizingSchool!

Sunny regards, 

Anne Deacon Juhl 

P.S. If you would like to learn some anodizing basics, have a look at this blog post in which I give an easy to understand introduction.


How to Define the Hardness of Hard Coat Anodizing

We are moving our blog! Anodizing World will still be available, but new posts will be published on aluconsult.com from now on.

To read the blog post "How to Define the Hardness of Hard Coat Anodizing" please click here.

Anodizing Aluminum: What it is and Why I love it

We are moving our blog! Anodizing World will still be available, but new posts will be published on aluconsult.com from now on.

To read the blog post "Anodizing Aluminum: What it is and Why I love it" please click here.

Join the Free Webinar about Hard Anodizing

Dear Anodizing World readers

Happy New Year! 

As you know, AnodizingSchool was launched in 2020 as a new learning community for anodizers and end-users of aluminum anodized products.

The aim is to create a one-stop online space, where you can get access to articles and webinars for free, but also buy specialized e-learning courses.

We currently offer the Anodizing Masterclass, and in 2021 we will publish new courses about Hard Anodizing, Pulse Anodizing and Anodizing for End-users.

The first event will be a FREE webinar about Hard Anodizing!

The webinar will be a guide to Hard Anodizing, also called Hard Coat including the following topics:

  1. Intro to Hard Anodizing, also called Hard Coat
  2. The history of Hard Anodizing
  3. How to create a Hard Coat
  4. Properties of a Hard Anodized surface
  5. How to specify a Hard Anodized layer
  6. What defects and other problems arising from a Hard Coated Surface
  7. Some Key takeaways and Q&A

Reserve your spot by sending an email to info@anodizingschool.com

If you find this article useful and you would like to know more please contact me info@anodizingschool.com

Get 3 amazing benefits!

Introduction to Anodizing 
has evolved and is changing its name to 

Anodizing Masterclass 

All 12 modules of the masterclass is now available! 
Learn the Better than Best practice of aluminum anodizing and bring your anodizing process to the next level!

Take a look at Anodizing School to read more about our aim to create an new online learning community for anodizers and end-users of aluminum anodized products. 

Interested? Get 3 amazing benefits if you sign up now

First, get a FREE 1-2-1 call to take the temperature of your anodizing process and identify the full potential of your line.

Then get access to FREE lessons from the Anodizing Masterclass!

And lastly, get the Christmas discount 25% of your purchase


Follow the link below to read more about the full course

Use the code CHRISTMAS to get a 25 % discount when purchasing the online course Anodizing Masterclass. (Offer expires on 24th of December.)


Influence of temperature on Voltage response when Anodizing

A question from a customer:

We have investigated the influence of the electrolyte temperature in our anodizing tank - Anodizing at a low and a warm temperature, current controlled and in our standard anodizing electrolyte.

The voltage at the higher temperature runs with a lower value than the voltage with the lower temperature and at the same time the voltage stays constant for the duration of the anodizing process. 

At the lower temperature the voltage keeps rising until we turn of the power. 

Do you have an explanation of why the voltage at the higher temperature stays constant, although the layer thickness is identical with both temperatures (with identical current settings and anodising time)?


Higher temperature in the anodizing electrolyte leads to higher conductivity, which means lower voltage for same current and time.

So your Vhigh temp is lower than your Vlow temp


Then Ohms law gives you             V = R x I

Vhigh temp = Rhigh temp x I

 Vlow temp = Rlow temp x I


I = same for the two temperatures


The total resistance of the electrical circuit consists of several resistances:


High temp:


Rhigh temp = Relec, high temp + Rthickness, high temp + …..


Low temp:


Rlow temp = Relec, low temp + Rthickness, high temp + …..


Lower temperature gives lower conductivity, so Relec, low temp ˃ Relec, high temp which is the reason for a higher Vlow temp

Higher temperature of the electrolyte will lead to faster chemical attack of the formed aluminum oxide changing the structure of the formed oxide and the resistance Rthickness, high temp

This will lead to an equilibrium thickness, where formation rate of oxide = dissolution rate of oxide leading to a constant voltage.

Lower temperature of the electrolyte will lead to a higher V0, low temp than V0, high temp for same current I.

The coating weight of the oxide layer is higher when formed at lower temperature - more compact and by this Rthickness, low temp will be higher than Rthickness, high temp. 

This is the reason for a continues increase in Vlow temp during the process time but eventually you should see a steady voltage here too.

If you are curious and want to know more about temperature, voltage and other parameters when anodizing in sulfuric acid you should sign up for the first and only online anodizing course!

Introduction to Anodizing - Click here!

If you find this article useful and you would like to know more please contact me 

Spangle on etch aluminum EN AW 6063

The spangle effect on the aluminum EN AW 6063 alloy has been known for many years.

There are still a lot of unanswered questions but more recently explanations have thrown light on some of the issues. 

The spangling effect on aluminum can be divided into three categories: grainy, galvanizing and sparkling.

The type where the grains are visible by the naked eye after etching is called grainy. Galvanizing is used when only few of the grains are shiny, and the sparkling is when the whole surface is shiny.

The first picture shows a EN AW 6063 aluminum alloy directly from extrusion - not a very beautiful appearance and with a lot of die lines - looking closer you can maybe see some of the grainy structure already. 

The next picture shows the surface after etching and anodizing. Here a very grainy structure is seen leaving to a very unattractive surface - especially if it should fit together with areas which are not having this surface appearance.

If you as a designer want to create something special - this could be a very interesting surface appearance to work with.

Well, back to the subject - why do we see this spangle effect on anodized aluminum.

There are two reason to look for - the first one is the content of zinc (Zn) in the etching tank and the second is the content of Zn in the aluminum alloy.

The grainy appearance is caused by the chemical composition, whereas the two more shiny appearance are due to the content of Zn in the solution and grain orientation.

The orientation of the grains has an influence on how much they are etched in the alkaline solution. Zinc is more noble than aluminum so in the alkaline solution there will be a selective dissolution of aluminum. This will lead to a higher concentration of Zn in the grains with a certain orientation creating small galvanic elements from grain to grain.

If at the same time there is zinc in the alkaline solution, even as little as 5 ppm can cause spangle under the right conditions.

Addition of a small amount of sodium sulphide can be used to precipitate the zinc decreasing the spangling effect of the aluminum alloy.

The EN AW 6063 itself should not contain more than 0.03% zinc.

If you want to know a lot more about anodizing and defects

Please sign up for more information regarding the first and only online anodizing course - Introduction to Anodizing presented by the Anodizing School.

If you find this article useful and you would like to know more, please contact me