Anodize: The Fast and The Furious

FAST.  When it comes to colored anodize, a key property to consider if “fastness.”  Oxford Dictionary defines fastness as the ability of a material or dye to maintain its color without fading.  The organic dyes used to impart color to freshly anodized aluminum are typically rated for both light and heat fastness on a scale from 1 to 10, poorest to best, derived from ISO 2135.  These ratings are especially important for architectural applications where sunlight exposure is unavoidable.  For these extreme applications, only dyes with a rating of 8 or higher should be used.  For example, Anoplate’s present black dye has a rating of 9.

FURIOUS.  Around 2006 Anoplate was approached by a lighting manufacturer who wanted their 2-piece “snoot” housing black anodized.  It was a straight forward 6061-T6 alloy and seemed like an every day job.  We did a couple of thousands of these and everything seemed cool (pun intended!).  About 3 months later I received a disturbing E-mail from the manufacturer.  Their customer was a prominent clothing manufacturer opening their first flagship store on Fifth Avenue in New York City.  Their lights used to illuminate the classis white polos were making the shirt appear copper-tone or pink.  As it turns out, the dye was fading within weeks.  The clothing store’s building manager and the lighting firm were furious.

Anoplate reached out to our dye manufacturer and returned several parts for their analysis.  They determined the anodize was of sufficient thickness and properly sealed.  They analyzed the dye bath itself and found nothing suspicious.  However, when they asked about the lighting source, they weren’t surprised to hear that we were dealing with halogen lamps.  Halogen lamps are twice as hot as a standard incandescent bulb and can reach temperatures in excess of 1,000 F.  The fading the customer was experiencing was simply a design issue – black anodize or most dyed anodize can’t withstand temperatures this high.

Unfortunately, I’m not Paul Harvey and I don’t have the rest of the story!  What I can say is the lamp manufacturer went to an alternative, higher cost blackening and ended up replacing thousands of lights.