I copied and pasted your post to chat GP
- I agree with it!
“You’re right to pause before doing anything aggressive—this is exactly the kind of situation where trying to “perfect” it can backfire.

Don’t iron it
Even on low heat, ironing is risky:
• Heat can set creases permanently rather than remove them
• It can alter or darken inks, especially on cheap posters
• Paper can become brittle or shiny
• Any hidden moisture can cause cockling or warping
In conservation/framing practice, ironing is generally avoided unless you’re trained in paper conservation with proper equipment.
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Your current plan is solid (and professional)
Leaving it under weight for a week and then hinging is a very sound, conservation-friendly approach.
You could refine it slightly:
1. Controlled flattening (better than just boards)
Instead of just boards, consider:
• Interleaving with acid-free tissue or blotting paper
• Then placing between clean boards with even weight
• Leave for several days to a week
This helps absorb minor moisture and relax fibres more gently.
2. Gentle humidification (only if you’re confident)
If the creasing is severe and you want to go a step further:
• A very light humidification chamber (not direct water contact) can relax fibres before flattening

But only do this if you’ve done it before—otherwise skip it. It’s easy to overdo.
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Hinging approach (especially with missing corner)
Given the damage:
• Use Japanese paper hinges + wheat starch paste
• Consider a float mount so the missing corner looks intentional rather than hidden
• Or use a window mount with spacing so it doesn’t press the poster flat unnaturally
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The key judgment call (this is the important part)
You said it yourself: “the customer understands it has had a hard life.”
That’s actually your biggest guide.
There are two valid outcomes:
1. Preserve character → light flattening, visible creases remain
2. Reduce damage as much as safely possible → gentle flattening only, no aggressive intervention
Trying to make it look “new” is where things go wrong.
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What I would do in your position
• Skip the iron completely
• Flatten under weight with interleaving
• Hinge using conservation methods
• Possibly float mount to embrace imperfections
• Explain to the client that you’ve preserved both the object and its history
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One extra pro tip
Before proceeding, you could even send the customer two quick options:
• “Minimally treated, retains character”
• “More flattened, but still conservation-safe”
That builds trust and protects you from over-restoring something sentimental”