Posted 04 October 2012 - 01:17 PM
The short answer, there are differences from batch to batch for bright anodized rings.
The long answer, for each color we have two anodized coils as samples to match a particular color that are a shade apart, one lighter/one darker, which are our guide lines. Part of my job is managing the anodizing line (a line of 36 sequential tanks roughly 12 ft long x 5 ft deep x 30 in wide containing cleaning solutions, caustic or acid solutions, dye colors, and seals) for our rings. When I first started anodizing I thought that I should be able to get the identical color from batch to batch, since then I have been severely schooled. Anodizing is a combination of art and science. The process involves multiple individuals working different sections of the line with each of them having to coordinate with the others to create a color. Factors include ph values of acids, bases, rinses, and seals that are constantly changing due to a factor called “Drag” (as an anodized piece goes down the line from one tank to the next it retains some of the fluid from the previous tank as it goes into the next tank) which alters the ph value of the various tanks, thus affecting the final color. In addition there is anodizing time for each color that varies on the color required. Furthermore, the dyes used are organic and over days or weeks the dye absorption properties change to a point where it becomes contaminated (mold forms) and we have to make a new tank of dye. These are the main obstacles but there are even more things affecting the final color. Home anodizing kits avoid many of these problems as the quantity of aluminum being anodized negates a lot of these issues. I compare our anodizing process to trying to bake a cake but you have to mix the ingredients in the backing pan, in the oven, while an invisible person adds and subtracts some of the ingredients and get the taste exactly the same each time.
On a related subject, some forum members have brought up occasional aspect ratio differences. This is rare and happens mostly with 20g wire rings if we don’t get the color correct the first time. To strip the anodized coating and re-run the batch thins the wire slightly but we have this happen less than 1% of overall production.
BTW I like the work you did on you corset/dress.
