Author Topic: How Does a Poster Darken?  (Read 537 times)

Offline bigmike

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How Does a Poster Darken?
« on: December 24, 2020, 05:51:17 AM »
Just curious on how an older poster would darken overtime? I know fading the poster colour becomes dull and is from excess light. But what would cause a poster to darken?
Could those affects of a darkened poster be reversed if cleaned and linen backed?

Online 50s

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Re: How Does a Poster Darken?
« Reply #1 on: December 24, 2020, 08:30:06 AM »
Fading not just UV light, but equal contribution also from cycling (eg daily) temperature changes.

Darkening of older posters is largely due to the acid content in the paper pulp, with low quality Mexican and Italian posters suffering greatly. The folds seem to speed the browning, not sure why but maybe the edges, if posters stacked, receive the temperature fluctuations more.


Offline bigmike

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Re: How Does a Poster Darken?
« Reply #2 on: December 24, 2020, 08:32:47 AM »
Is there anyway to prevent the darkening?
Once it darkened, is it reversible with cleaning and linen backing?

Online 50s

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Re: How Does a Poster Darken?
« Reply #3 on: December 24, 2020, 08:49:30 AM »
To help prevent the darkening, I'm not sure if flattening it would stop the spread from the folds as thinking about it, it might also be a result of paper fibres bending or breaking increasing the acid spread somehow, not sure. Keeping it in a close to constant temperature would help. You could clean it as you mention, but also at the time of linen backing I believe you can also try to somewhat deacidify the paper thru some liquid treatment (I'm not expert). Bleaching also at that time will brighten a bit the whites, but also fade a bit the colours, and it deceivingly looks better because the white brightens more than the color fades.

Offline bigmike

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Re: How Does a Poster Darken?
« Reply #4 on: December 24, 2020, 08:57:52 AM »
If I keep them individually on their own acid free backing boards (that say they trap and neutralize the acids). Do you think that would help or prolong it from darkening... I donít want to have to linen back all my Italian posters...

I was mainly curious because EMP had an upcoming auction I want to bid on, but the poster has darkened already.. if it could be repaired with cleaning then backed.. but now that you mention about the Italian posters now has me worried.

Online 50s

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Re: How Does a Poster Darken?
« Reply #5 on: December 24, 2020, 03:55:59 PM »
I don't think acid free boards do anything like trap and neutralize acids. They are just a barrier say between other posters, and being acid free, the board shouldn't contribute to adding more acid into the poster

Another related thought, PVC tubes for containing rolled posters is supposed to be not good as gases leak out affecting posters somehow

The acid not only browns the poster, it makes it more brittle over time so the poster over time will turn to confetti, starting with tearing. Linen backing with washing and de-acidifying, (backing also helps protect against dings/bump damage and damage from repeatedly folding and unfolding ) plus keeping it away from direct and reflected sunlight (UV) and keep in a constant temperature environment I think would be the way to preserve it best, even though linen backing does its own damage, supposedly is irreversible due I assume to it getting stretched a bit in the process and saturated with glue paste.

If I see a poster for sale showing evidence of browning (foxing) I am quite dubious because good lighting or camera flash can hide much of it, meaning it could be worse than expected.


Offline bigmike

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Re: How Does a Poster Darken?
« Reply #6 on: December 24, 2020, 04:13:22 PM »
What are your thoughts from bagsublimited boards where it says this?
ď Standard Acid-free is acid-free all the way through. Acid-free board can trap migrating acids in paper and neutralize it. Use our .028' thick board for intermediate to long-term storage. White on both sides.Ē?

I think bainbridge boards say something similar as well?

Offline CSM

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Re: How Does a Poster Darken?
« Reply #7 on: December 24, 2020, 06:41:43 PM »
What are your thoughts from bagsublimited boards where it says this?
ď Standard Acid-free is acid-free all the way through. Acid-free board can trap migrating acids in paper and neutralize it. Use our .028' thick board for intermediate to long-term storage. White on both sides.Ē?

I think bainbridge boards say something similar as well?

I think go for it 😉
Chris

Offline bigmike

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Re: How Does a Poster Darken?
« Reply #8 on: December 24, 2020, 09:21:37 PM »
I think go for it 😉

I think I will for the smaller size posters. Older one sheets. But 50s got me worried about the larger Italian and French posters I have now ;) eyeroll

Online 50s

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Re: How Does a Poster Darken?
« Reply #9 on: December 25, 2020, 12:43:33 AM »
French ones aren't so bad, it was Mexican and Italian I find are on poor paper that foxes easily. I don't think backing boards are going to suck enough acid out of the poster to make any difference to the poster

Offline bigmike

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Re: How Does a Poster Darken?
« Reply #10 on: December 29, 2020, 07:34:53 PM »
You got me to the point if I see any of my older Italian posters start to darken, they go to my linen backer now. eyeroll
Iíve been looking at deacidification sprays, but they become costly...

Offline ealingmovieposters

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Re: How Does a Poster Darken?
« Reply #11 on: January 01, 2021, 10:06:04 PM »
For Mexican posters in particular - I would add:-

To be 'very' cautious using any bleach on these posters which were made of 'ligneous' paper (due to the manufacturing\machine method of pulping, rather than a chemical process) - especially 'Oxidizing Bleaches' as Calcium Hypochlorite is the only oxidizing bleach which can be used with lignin containing papers - https://www.conservation-wiki.com/wiki/BPG_Bleaching. Personally, I would not bleach any 'woody\ligneous' paper and would do a lot of research on the paper of any poster I was considering bleaching.

That said, If anyone else has experience using bleaches on Mexican\Argentinian posters from the 1940-1970's, I would appreciate any insights.

Offline okiehawker

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Re: How Does a Poster Darken?
« Reply #12 on: January 04, 2021, 11:38:37 PM »
If I keep them individually on their own acid free backing boards (that say they trap and neutralize the acids). Do you think that would help or prolong it from darkening... I donít want to have to linen back all my Italian posters...

Hi Big Mike, Acid free boards that have pH buffering impregnated in the board are archival and are used to help neutralize acidic conditions when stored with paper (e.g. posters, comics, pulps, famous documents, etc.). With extremely unstable pulpy paper that's valuable, I think it's a good idea to have it washed and during that washing impregnate the paper with pH buffering capacity. Then, to limit free oxygen and humidity fluctuations, store well in Mylar, a tight poster/map case, and/or framed. If a poster already looks pretty good, I think you can just store or frame it well and you'll be fine. I have posters that are near 100 years old that are just stored well and even in the humid south U.S. where I live look to have not aged since I've had them.  Best, Okie

Offline ealingmovieposters

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Re: How Does a Poster Darken?
« Reply #13 on: January 05, 2021, 11:25:20 AM »
Ref my previous comment on bleaching - Whoops, my typo the recommended bleach to use should be - Hydrogen peroxide - NOT Calcium Hypochlorite  - for ground woods papers:-

 Quote- https://www.researchgate.net/publication/281271851_Reducing_the_Risks_of_Hydrogen_Peroxide_Bleaching_in_Presence_of_Iron_Ions_in_Paper

Hydrogen peroxide  is nowadays one of the most common bleaching agents in paper conservation due to its easy handling, its low toxicity and the wide range of application options. It can be applied in different concentrations ranging from below 0.1% to 3.0%, which is usually considered the upper safe limit. It can be used highly localized, but can also cover broad areas of the paper. The treatment duration can be greatly varied. Also, in contrast to chlorine-based bleaching agents, H2O2 can be used for ground wood papers as it increases their brightness without removing their ligne-ous components.
End-Quote

Offline bigmike

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Re: How Does a Poster Darken?
« Reply #14 on: January 06, 2021, 05:45:37 PM »
Thanks for the input. Most of the ones I have are in good shape. The older Italian ones, I bought already are fragile, and I just may get those backed. But if the ones that look good. I may just buy the acid free boards for them.