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topic 10625

Pylumin finishing for aluminum and aluminium alloys


We produce avionic instruments. Some very old drawings, for pieceparts, call up an aluminium alloy finishing process referred to as "Pylumin". The resulting color apparently was uniform grey to black. The process supposedly imparted increased corrosion resistance and an excellent base for paint. I require an alternative and have tried the www without success. Can you offer an explanation as to what the process entailed and is there a modern equivalent process.

Victor Arghyrou
aerospace - Plymouth, Devon, England


Could not find pylumin anywhere, but Mohler, in "Electroplating and Related Processes" [link is to info about the book at Amazon], says 'Bengough and Stuart process (chromic acid) anodizing was applied for protection of seaplane parts. 3% chromic acid at 100 to 115 F. The color of chromic acid anodizing fits the grey to dark grey range. British Patent 223,994 (1924)

tom pullizzi monitor
Tom Pullizzi
Falls Township,


I have pylumin listed as an alkaline chromate bath for aluminium, from "Phosphating & Metal Pretreatment" [link is to info about the book at Amazon] by D B Freeman.

A little while ago a customer of mine enquired about the process and I found out that at that time, only 1 company was using the process in the UK (an in house defence contractor). If I remember correctly I had to get in touch with a chemical supply house called pyrene to get more info. Though since then I believe they've been incorporated into another organisation.


Richard Guise
- Lowestoft, U.K.


As BAE (SYSTEMS) and AIRBUS (I hope that is the right name for this week) are our largest customer I feel obliged to help.

If you cannot find this coating by name we will have to go back to the design stage question asking.

What is the aim of the coating? Are we going to paint on top?

Are there size allowances on the drawing for the coating? If there are it can tell me if you have a chem film or anodise coating.

As the drawings are so old I take it this a spares contract so volume is going to be low so it might be the case to give it the best finish you wish as you are going to hit min batch price so the price advantage of chem. film to anodise does not matter.

Please come back with more information and hopefully you can find the right answer for these parts.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


If the name is Pyrene the company is now Chemetall based in MILTON KEYNES, ask and you will find a person who been there for years he may well have the answer.

Martin Trigg-Hogarth
Martin Trigg-Hogarth
surface treatment shop - Stroud, Glos, England


In the U.S.A. Chemetall/Oakite. They may be able to cross reference the product.

tom pullizzi portrait
Tom Pullizzi
Falls Township, Pennsylvania

November 24, 2009

Pylumin Process; aluminium immersed in sodium carbonate (7%), sodium
chromate (2.3%), basic chromium carbonate (0.5%) plus sodium hydroxide
(0.5%) solution at 70 C. Resistance coating used as a paint base.

trevor Southwell
- Havant.Hants.England

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