How Long Does It Take Yellowing Decals To Whiten?

[Miatatom]

I build mostly race cars so obviously, there's a lot of decal work. I've got two sets taped to a window to get rid of the yellowing. In your experience, how long have you typically had to leave them exposed to sunlight in order to get rid of the yellowing?

[Snake45]

IIRC, you should be able to see some lightening in a couple of days, full bleach-out can take a week or more. As always, your mileage may vary. 

If there's no change at all after a week, it's not gonna work. 

You want to make sure the window gets plenty of direct sunlight. I've had good luck thumbtacking decals to a piece of cardboard and then putting that in the back window of my car (package tray). 

I've had VERY good results with sun-bleaching decals, I think I've only had one or two sheets where it didn't work. Good luck! 

[Exotics_Builder]

1 hour ago, Snake45 said:

IIRC, you should be able to see some lightening in a couple of days, full bleach-out can take a week or more. As always, your mileage may vary. 

If there's no change at all after a week, it's not gonna work. 

You want to make sure the window gets plenty of direct sunlight. I've had good luck thumbtacking decals to a piece of cardboard and then putting that in the back window of my car (package tray). 

I've had VERY good results with sun-bleaching decals, I think I've only had one or two sheets where it didn't work. Good luck! 

As Snake said.  it may take a week or a bit longer (depending on weather) to get a full bleach out

 

[Miatatom]

Thanks guys! I'll be patient. ?

[Mike999]

Anybody ever had decals re-yellow?  I was recently looking for info on using old decals, and found this 2008 thread at the ARC Discussion Forums:

"...putting yellowed decals in UV light to bleach them does work, but it's not permanent. They turn yellow because of organic compounds in the clear carrier film of the decal. The yellowing is oxidation, which cannot be prevented. 

Organic compounds in contact with oxygen will oxidize, and in this case, yellow. So put them in the window and bleach them, but be aware that even if you 'seal' them with Future, they'll still be exposed to oxygen in the atmosphere, and thus will yellow again over time (on your model). Just so you know."

http://www.arcforums.com/forums/air/index.php?/topic/171670-hasegawa-decalsare-they-ok/

[Miatatom]

2 hours ago, Mike999 said:

even if you 'seal' them with Future, they'll still be exposed to oxygen in the atmosphere, and thus will yellow again over time

I wonder if spraying clear over the decals to seal them after they have been applied would prevent this?

[Exotics_Builder]

20 minutes ago, Miatatom said:

I wonder if spraying clear over the decals to seal them after they have been applied would prevent this?

In my experience yes.  One of the reasons I clear over decals.  I did a BMW M 635 CSi Schnitzer years ago that had layers of decals.  I did not clear over and they yellowed over time.  Lesson learned