Date: Tue, 15 Jan 2013 12:41:40 From: Terry Stewart <terry at webweavers.co.nz> Reply-To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> To: "General Discussion: On-Topic and Off-Topic Posts" <cctalk at classiccmp.org> Subject: Re: Retr0Bright: Does re-yellowing occur even in the absence of UV light? Yes, as far as I know that is correct, but I'd always assumed (maybe wrongly) that a reasonable amount of UV light was needed to facilitate this. Based on what's happened it may be that very little UV (if any) is needed. In the case of my Retr0Brighted cases....just a few days exposure per year under florescents (i.e. the time I had the computers out of the box to play with or test) seemed to be all that was needed. Merlin, in his writeup in the Retr0Bright wiki (http://retr0bright.wikispaces.com) does say even low levels from florescent lights is enough. I'd always assumed this was everyday exposure though. Perhaps with some plastics UV is not needed at all? I have heard of cases where people have put a shiny white computer in a sealed box for storage only to find a cheese-yellow artifact when they drag it out years later. There is something more puzzling. Let's assume yellowing can occur in the absence of much (or any) UV light. Why then are those cord markings on the Apple IIe and Vic 20 reappearing? You would have expected any further yellowing of my cases, even with low levels of UV, to be consistent across the case surface now the cords are not there. All surfaces would be exposed to equal amount of oxygen or brief light. However the cord impressions (which protected the plastic under them from initial yellowing) are re-appearing?

from the case itself. Even a single sheet of paper would partially

The question I have in my mind therefore is "do the changes in the chemical structure cause by the initial yellowing (OR perhaps the RetroBrighting itself) make the plastic MORE prone to future 2BR.O co-ordinant bonds or/and migration of these to the surface of the case (hence causing yellowing)? " Or is something else going on? Whatever is happening, the practical implications are that even brief and very very low levels of UV seem to be enough to re-yellow retr0Brighted surfaces over time. There is not enough evidence in my case to say that UV is not needed AT ALL, as all the units had been exposed briefly a few times a year, to fluorescent light. Tez

know how you would do that) Retr0Bright is only ever going to be temporary.

Yes, as far as I know that is correct, but I'd always assumed (maybe wrongly) that a reasonable amount of UV light was needed to facilitate this. Based on what's happened it may be that very little UV (if any) is needed. In the case of my Retr0Brighted cases....just a few days exposure per year under florescents (i.e. the time I had the computers out of the box to play with or test) seemed to be all that was needed. Merlin, in his writeup in the Retr0Bright wiki (http://retr0bright.wikispaces.com) does say even low levels from florescent lights is enough. I'd always assumed this was everyday exposure though. Perhaps with some plastics UV is not needed at all? I have heard of cases where people have put a shiny white computer in a sealed box for storage only to find a cheese-yellow artifact when they drag it out years later. There is something more puzzling. Let's assume yellowing can occur in the absence of much (or any) UV light. Why then are those cord markings on the Apple IIe and Vic 20 reappearing? You would have expected any further yellowing of my cases, even with low levels of UV, to be consistent across the case surface now the cords are not there. All surfaces would be exposed to equal amount of oxygen or brief light. However the cord impressions (which protected the plastic under them from initial yellowing) are re-appearing? The question I have in my mind therefore is "do the changes in the chemical structure cause by the initial yellowing (OR perhaps the RetroBrighting itself) make the plastic MORE prone to future 2BR.O co-ordinant bonds or/and migration of these to the surface of the case (hence causing yellowing)? " Or is something else going on? Whatever is happening, the practical implications are that even brief and very very low levels of UV seem to be enough to re-yellow retr0Brighted surfaces over time. There is not enough evidence in my case to say that UV is not needed AT ALL, as all the units had been exposed briefly a few times a year, to fluorescent light. Tez