Artwork Cockling.

[Justintime]

Not so much an ask for help as a "anyone else suffering from this at the moment"?
I'm lucky enough to have a reasonably stable relative humidity in my studio, currently sitting at 45%, which is within the perfect museum range of 40-50%. However the temperature is less controlled. In winter I can regulate it around 20oC but in Summer and particularly recently it has spiked to 28oc for a number of hours each day.
I took a print in a few months ago which I remember being perfectly flat. the customer returned to do a redesign a month or so later and I noticed that the paper had a very mild cockle to it. Now it's finally time to mount it, it has a more much obvious cockling going on.
After a long chat with Google AI I have learned much more about the reasons and causes of this development, much of which I don't think are discussed enough in our circles. I'm going to assume that the information and remedial advice is correct, but also double check it with a few top tier framing experts before undertaking the remedial work suggested.
Anyone else suffering unexplained cockling?

[vintage frames]

That sounds really interesting.
Looking forward to hearing how you're going to deal with it.

As a further comment which will be of no help whatsoever,
the cocking effect appears unique to only modern production papers.
Early cotton rag or hemp papers seem to get along quite happily in any sort of climate.

It might be something in the way they sort of breathe by soaking up the humidity and then drying out again as the climate changes.
A bit like a lime mortar building.

[Justintime]

It is partly that. In this case the print image on the paper is an inkjet UV curing process, so it's slightly plasticised. Part of the problem sounds to be that as the RH dropped (when it entered my drawer) the outsides of the print dried out quicker than the reverse centre of the print (as the plasticised image front cannot "breathe", only the reverse of the paper ) which initially caused the minor cockling. Followed by a steady rise in temperature, up to 28oc, this exacerbated the problem causing more extreme cockling to develop. Contrary to what I have heard in the past, AI says that it is permanently reversible, but will not reverse over time once it is sealed in a frame. I'm told it has to be forcibly reversed, by for example 20 minutes under cold vacuum, immediately followed by up to 72 hours under weighted glass, preferably plate/toughened. This will apparently force the fibres back to their original length and it should remain flat if framed straight after, unless of course it is subjected to extreme heat or humidity change again, but once framed the effects will take much longer. The processes I mentioned have been greatly simplified for ease of reading this!

[vintage frames]

Well, you could try it out. You've got a vacuum press.
Pop a few sealed bags of ice in with it, if its a cold vacuum needed, then go for the 72 hour press.
I can't see what damage it could do.

[Justintime]

Like a cold pressed coffee??

[Justintime]

So, more details for anyone interested, although it's a bit of an echo chamber around here these days, but for posterity here goes...
The print is from The Tate Online shop, inexpensive at £40 for a 600x560 paper size and what they call "custom print", what the rest of us call "print on demand". After some research I have found these prints are "UV cured" meaning for us that the image on the paper has a plasticised coating. The short of it is that this is relevant because it causes the outside border of the art paper to expand and contract at a different rate from the centre of the paper where the plasticised image is. In fact the image area of the paper can only change with the humidity changes on the reverse, as the front of the image is basically sealed from the atmosphere.
After much discussion with AI and agreement from a human framing trainer (thanks Jon Price), I put the print into the Hotpress vacuum press without heat (because of the plasticised coating), initially 20 mins under vacuum, the order being foam, mountboard, print, release sheet, mountboard. It was then placed under glass and weights (approx 30kgs) for 24 hours. That sandwich comprised of 18mm ply, 2mm glass, the hotpress package as before, 2mm glass, mountboard and weights. The result was disappointing so I repeated the vacuum press procedure for an hour and returned it to the weights sandwich for a further 72 hours. Sadly the difference was negligible and I have ordered a new copy of the print.
I realise that I could have saved a lot of time and ordered the new print last week, but what would be the fun in that!
I have very successfully flattened hand made prints in the past with a medium heat between mountboard in the hotpress. I have now unsuccessfully flattened a UV cured plasticised print without heat. It was a useful experiment and one that I hope saves someone a bit of time in the future.
Also if someone tells you that you can flatten paper but it will always return to that cockled state eventually, which is what I was told, my research says that's wrong and if flattened and hinged and sandwiched straight away then subject to it being displayed correctly, in the correct temperature and humidity it will remain stable in that state. Paper can be forced back to its flat shape, but not when its partly plasticised, is my take away.

[vintage frames]

So what happens now, Justin?

Do you explain to the customer that their 'custom print' is just cheap, mass produced printing and is always going to go wobbly or do you fit a fresh new print and then have to warn them that the print, by its nature, may exhibit a degree of cockling in the future, depending on climate and relative hunidity in their home?

[Tudor Rose]

Not at all surprised by the results you got from the Hot Press.

If all you are doing is effectively trying to squash it flat - either with weights as you then did or a vacuum press as you tried initially - you are not relaxing the fibres to get the paper itself flat in any way.

The only method I've heard, that Steve Goodall and others have talked about when using the Hot Press, involved increasing the humidity within the press itself as part of the process. Obviously not a great option for you with this piece, but doing it dry was never going to change anything. Whatever AI or others may suggest. After all, as we've seen on other discussions on here, AI will often bend itself to agree with what it thinks you want to hear!

If you were on a hiding to nothing as you thought, then a gentle rehydrate etc etc might have been worth it (not using a Hot Press at all) - but buying a new print is the most logical solution. Glad you were able to get it done for your customer.

[Justintime]

The customer has been informed at every stage and consent was given for the flattening work. She mentioned it was a gift, so whilst I discovered that it was a £40 print, I was careful not to discuss the value with her but did have her confirm with the giver that it was from the online store I had found.
As I don't discount my work, I can take a hit like this.
The theory is that once a print is hinged, mounted and taped in a sandwich, then changes in humidity and temperature have a much slower (and therefore reduced) effect on the paper. In all likelihood if the replacement print arrives without cockling and is framed immediately, then it should stay that way if treated correctly, for many years to come.

[Justintime]

Thanks Jo, you got in before I sent my reply to Dermot.
I agree with everything you are saying, there were just too many limitations with this kind of print.