A rule of thumb for mould/weight calc?

[Starboard]

Again, newbie alert!

A client has a nice poster (print on paper) they want to protect using a TrueVue glass, low reflection and 70% UV protection. Was thinking 3mm thick as this is a larg-ish piece of glass.

Artwork is 1000x600mm, they don't want a mount. Glass would weigh 4.5kg/10lbs (with 3mm thickness), mould and backing only adding a few grams to this.

The mould they like is a 20x20mm section:

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Question is, in your opinion, is this profile strong enough to take the weight?

Is there a simple rule of thumb to calculate required mould section depending on total weight?

Also, would there be any reason not to place the glass directly in contact with the printed artwork?

Thank you for your help

[prospero]

IMHO 2mm thick glass would be fine for something that size. With 3mm all you are doing is making it heavier.

For a frame of that profile I would add a hefty subframe and let that take the weight.

As for direct contact, OK(ish) if the work is drymounted. There is alway the risk that it will stick to the glass.
Spacing it away is always a good idea.

If you simply plonk it in the frame without a mat then it will go wavy very quickly.

[Gesso&Bole]

Agree with Prospero, I would use 2mm

As for moulding, I would say no to the customer, and if they want the 20mm face, go for something 40mm deep. Even then, it might need a subframe unless it is in Oak or similar.

Let me re-wind here. What the customer wants may well be entirely possible, in fact I'm sure it is possible, but you are making life difficult for yourself, particularly if you are fairly new to this by trying to outwit the laws of physics. It's much harder work, and much less profitable fiddlig about trying to make an under sized moulding strong enough, rather than the customer paying for an appropriate size of moulding. A flimsy frame, that leaves your workshop, and gets broken before hanging, rather stays your problem.

Also, you mention that the customer wants to 'protect' the poster. Perhaps if you give more information here about the artwork, we can advise on whether dry mounting and close framing are appropriate or not.

[JFeig]

I have a question for my fellow picture framers across the pond regarding 2 mm glass.

Does your thinner glass come in any of the modern variants of glass used in the picture framing industry(AR, UV filtering, low reflection)? If not, then the 3 mm glass route is the only option.
The 2 mm glass that I see is only basic, unaltered float glass, straight from the glass manufacturing plant.

[JKX]

That’s a fortnight (too weak) moulding. But the same width in aluminium would be fine.

If you want to protect the print then it should not be touching the glass, also the 70% UV is not even worth mentioning protection-wise, it’s just a slight added bonus of the optical coating.

Acrylic would be acceptable as condensation is unlikely but the thing could still cockle unless dry mounted - so again, protection out the window..

And it’s mouldING not mould.

[Justintime]

@Jfeig Yes the Truvue and Artglass AR70 is 2mm.
Ditto to everything said above. The general rule of thumb with glass thickness is that under a m2 2mm is fine. There are exceptions obviously like a 1200x300 frame etc.
As Gesso&Bole said, assuming you're talking a hardwood like Oak or Ash I'd definitely go larger profile. My preferred for this wood be Rose and Hollis A115 Oak, it's a good thickness. It's all about whether the frame will flex or not and how you attach hanging hardware can affect this too. If using d rings and cord you definitely want two hanging points rather than one otherwise this can cause flex too. Heavy duty hangers like Lions 6594 for wall hooks rather than cord make you're job easy. You could have a really large Obeche/Ayous moulding that would be strong enough but if you put the hanging cord on wrong the pressures on the frame could flex it, problem.
If I'm close framing something, I hinge it to an equal sized piece of mountboard and use a paper wrapped spacer between glass and work. I have never put anything directly against glass, but very occasionally and only when necessary using acrylic glazing. The reason not to place work directly against glass is that during seasonal changes in temperature and humidity the inside of the glass can be affected by micro-condensation which would be transferred directly onto the artwork damaging it and as said before making it likely to stick to the glass. Acrylic is a much safer option as it is not such a good conductor of heat/cold.
I'd be careful offering AR70 as offering protection as 70% is not considered sufficient UV protection. UV99/Conservation Clear would be the best option for protection and price, AR99/Museum for best protection and anti reflection.

[Starboard]

Thanks for your input. There is an awful lot I need to learn.

Artwork is an old advertising poster on a thick-ish paper – really, the usual type of strong paper used for e.g. cinema posters of this 1000x600mm size. Problem is that client is hardly ever in London, took me ages for them to decide on the mould style (my fault for not anticipating the weight/structure issue). So I am really trying to work around this.

• 1/ I understand the idea of dry mounting to keep the poster flat. As I do not have a press, I believe that a self-adhesive board is the way to go. Bit nervous about doing this, but one has to learn at some point.
  2/ 2mm glass instead of 3mm makes sense (and saves quite some weight). @jFeig: it looks like you have many UV glass choices in 2mm in the UK.
  3/ Sub frame: even if glass is only 3kg when using 2mm glas, that's still some weight. How can I make a subframe that would not be visible under this 20x20mm? Any video tutorials you would know? Not sure how I could fit a subframe under this thin 20x20 mould.
  4/ Well noted the remark re: spacer. Thinnest are 1.5mm. Plus my 2 mm glass, that only leaves 12.5 mm height available.

Again, thanks for your help!

[prospero]

It's not just the rigidity of the moulding on a thin section you have to consider. It's the area of the cut mitre that
denotes the area that is glued. If you put wire hangings on the frame the corners are under torsion. Not a huge
amount but constant. This can cause the glue bond to fail eventually and the only the pins will hold the joint together.
The pins will prevent catastrophic failure (i.e. falling to bits) but the mitres will gap and continued twisting increase
the likelihood of the whole thing failing. The larger the area the better chance the glue bond stands.

If thin moulding is called for - entirely possible, then you have to divorce the idea of the 'frame' doing all the supporting
and use a subframe, preferably with a thin moulding deep enough to swallow the subframe/art/glass. It doesn't matter too
much if it protrudes beyond the outer frame as long as it is not overtly visible from the side. The hangings are fixed to the subframe
and all the frame does is serve to hold the 'sandwich'' together. There is minimal stress on it.

There are available subframe mouldings (Wessex?) which are cunningly designed so that a French Cleat hanging system can be employed.

This is one a made for a giant-sized frame. It uses (quite cheap) 8mm thick pine cladding to make a relatively light but VERY
strong and stable structure that takes all the weight. The two-layer construction allows half-lap joints to be formed without the
irksome chiseling. Just a bot of glueing and screwing. The frame that went around it was in fact quite chunky, but I could have put a
very skinny one on without affecting the overall integrity.

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[Justintime]

1. "An old advertising poster" although perhaps of low financial value is probably irreplaceable. In which case I strongly advise you not to permanently mount it. Instead use a reversible technique by hinging it to a board with gummed (not self adhesive) hinging tape. If you insist on mounting it, DO NOT use your customer's work to practice on.
3. As próspero says, there is a subframe available from Rose and Hollis that is about 10mm deep which would fit. This photo from Hawkinsframing.com illustrates how it should look once fitted.
4. I don't know what spacer at 1.5mm you mean?? Spacer start at around 5mm depth. A 1.5mm slip of mountboard will not provide sufficient safe distance between the glass and work and will still likely damage the work. The recommended distance from the glass is 4-5mm when using a spacer. (A window mount has much more surface area holding the work in place so can be thinner.)
However difficult a customer is to get hold of, it is your responsibility to ensure that everything is designed correctly before commencing the job. Assuming that you have taken their details, it is simply a case of arranging a whatts app message/call/video to confirm changes in design cost etc. Obviously there are times when the customer doesn't need to be informed of certain changes and when you're happy to absorb the extra costs associated with them, but in my experience customers do not mind being contacted during the framing process in fact they usually like it.
I hope you're hearing the phrases like "catastrophic failure" etc. and are reading the room. If you're not 100% comfortable attempting any of this then stop and call one of us and we can talk it through. A piece this size and with this moulding is not one to make a mistake on.

[Starboard]

@Prospero @Justintime,

Fabulous, detailed answers. Thanks a million, really. Learning stuff – and I now have a proper 5-day training course lined up.

Went to visit Wessex framing supplies and finally seen in the flesh how a subframe works. This is the first and hopefully last time I will show clients an undersized moulding. Good job the community saved me from making a flimsy frame.

The moulding I have shown the client is also available in 30mm, which seriously increases the glueing area and give me a much deeper rabbet, which in turn allows for the sub frame to hardly add any extra thickness from the original moulding (+1.5 mm).

Would look like this:

One last question:

I dont plan to do a window mount on top of the poster. Is it safe for the spacer to be in direct contact with the artwork/poster? The very edges of the poster are not damaged, but they are a bit frayed on a couple of mils, being hidden behind the spacer would hide them. Or do i have to mount the poster on the mountboard (using gummed tape) so that it sits exactly ind side the footprint of the spacer?

Thank you

[Justintime]

There are differing views on this. I am happy to close frame the work behind the spacer, some are not. I hinge onto board, the top hinges are "tight" the surrounding hinges are "loose" (see Hedgehog technique) allowing for expansion and contraction of the work. If the backing board is not secured under pressure then I believe that the work can still move freely.
If conservation is important then everything coming into contact with the work must be conservation standard. The face of the spacer touching the work can be sealed with a white gummed tape or frame sealing tape, as can the inside of the frame, creating a conservation quality barrier between work and materials.

[Justintime]

On a piece that size I'd want a spacer deeper than 3mm. Standard spacers start at 5mm deep providing ample distance from the glass and can be joined on an underpinner using 3mm wedges. I wouldn't stress about the subframe extending a few mm more. If the subframe extended a lot more and you weren't happy with it, you could add an extension to the back of the frame as illustrated in a post I made yesterday.