@Heidi Mead
Below is the response from Jamie Hascall, Craftsman, Trainer, Consultant at MountMaking Focus
Hi Sharon and Heidi,
I've been looking at this question and trying to come up with a reasonable path forward for you. As I figured, it's going to take a little bit of explanation so please bear with me.
I feel that gluing acrylic is a bit of a black art. I have had very uneven results any time I've tried it and have never tried to fabricate vitrines as getting a clear glue line on a long running joint requires tooling and expertise that I do not have. It is one of the reasons vitrines are so expensive, and thus why your predicament is so urgent.
I'll start with the basics of gluing acrylic. The "glues" that are used to join acrylic are solvents that are actually softening the acrylic plastic to the point where the two sides weld together. (Generally Methylene Chloride or other very nasty solvents. They must be used with good ventilation and PPE.) In the process, the plastic swells, and then shrinks again. As joints age, that shrinking seems to continue and at some point they weaken and becomes much more prone to failure. Close inspection will show that the area of clean line of the joint will start to show little uneven edges or even voids within the joint. Failure is likely to start at the ends of the joints as it is the least supported point and will slowly progress from there. If a joint fails quickly on a new vitrine, it is likely a manufacturing defect such poor joint fit or insufficient annealing, a slow heating and cooling done after glue-up done to relieve stresses within the assembled box.
Your thoughts of temperature change as a cause of failure is reasonable, but I imagine that more likely culprit is the repeated flexing of the entire vitrine that occurs with the physical rubbing of cleaning. Given that there needs to be enough room between the accompanying stand or backboard to get the vitrine on and off and not have the shrink and swell cycle of each component cause damage, there is enough play that everything will inevitably flex and move a little. As with so many things, it is the cumulative effect of little actions that cause the most change. The acrylic sheet is an intrinsically flexible material and each time it is cleaned, some amount of force will travel to the edge where there is a very narrow and inflexible joint that is maybe 6mm wide. The leverage will be a significant multiplier of the force and with that in mind, it's a wonder that vitrines last as long as they do, and is a testament to the strength of a good glue joint.
So now, the question is how to proceed with a repair. One of the issues is that the solvent glues that are used are generally water-thin and require a very square and close fitting joint to provide the conditions for proper capillary action to draw the glue into the joint. This is why the fabrication of vitrines is so difficult. The damaged joint no longer has the clean surfaces and tight fit that will easily draw the glue into the joint and allow it to re-soften and weld. Thus, you'll need to use one of the slightly thickened versions of the cement to help fill gaps. (The cement is the solvent plus a little acrylic dust as a bulking filler.) I would recommend IPS Weld-On 16 as the best choice. (Super glue/cyanoacrylate glues will not work well with clear acrylic.) The hard part is that you've got a fairly close fitting joint that is still good and tight at the tip of the break so working in glue is not easy.
I would plan on having the vitrine on a bench for stability and ability to clamp it for a period of time. This repair will not be able to be done in-situ. I'd tape the corner just above the tip of the failure to keep that part of the joint supported. Opening up the broken joint from the bottom with a small probe should allow you to place a line of glue into the void and then let it come back together and clamp it until the glue has set. Any glue that is trapped under tape or a clamping caul will bond and mar the surface so you'll need to find ways of clamping that can stabilize the parts but not trap glue. If you possibly have a vitrine that is badly enough damaged that you will not be using it, you can use it as a test bed for your technique as it's going to take some learning to make this work well. Letting the whole thing set overnight will be important to let it gain strength needed.
I'm including some links to a list of the glues used and a Fabrication Resources page from Plaskolite plastics, one of the large manufacturers of acrylic. Their Optix Fabrication Manual is really good.
I hope that helps. Please post any follow up questions or get in touch with me directly if I can be of further help.
Good luck,
Jamie
Jamie Hascall
Craftsman, Trainer, Consultant
Mountmakingfocus.com
jamie@mountmakingfocus.com
Seattle, WA
206-954-4141
On Dec 2, 2022, at 8:11 AM, Sharon Fickeissen <sfickeissen@Hagley.org> wrote:
Hello Jamie & Rachael,
As the acting C2C Care community monitor, I am passing Heidi's related inquiries on to you, the C2C Care experts specializing in exhibit preparation and mount making. Heidi Mead, Vertebrate Fossil Preparator at the William P. Wall Museum of Natural History in Georgia posted this initial query:
I am wondering if any of you might have some insight into why our expensive vitrines might have suddenly popped open at the seams.
Our housekeeping methods for cleaning cases only involves a very lightly dampened cloth (distilled water). There is no crazing.
We do not move these pedestals, and they have been in place for close to ten years.
12 out of our 21 vitrines are exhibiting gaping at the sides, top, base, or all seams. There does not appear to be any one pattern. All cases are in the same room, some along walls, some centrally located.
The vitrines were purchased in lots from the same vendor, however the manufacturer may have differed. I cannot tell from our invoices.
We do use a data logger, however, due to an oversight, the logger has not been recording.
I am inclined to think this is due to some kind of environmental factor, like sudden temperature fluctuations. We had some sudden drops in the outside temperature. Without the data logger though....
I have spoken with the vendor from whom we purchased, and they are inquiring about how we might repair these. They did acknowledge that they no longer use the same manufacturer. This will be a huge task, and I would truly appreciate any thoughts any of you might have.
This is her more recent follow-up:
I am interested in attempting to repair vitrines that would exhibit natural history specimens. Does anyone have any recommendations for working with acrylic sheeting, adhesives, and museum specimens? I would prefer to work with materials and methods that are conservation approved, I just don't know where to look to find them! I poked around in the Materials Testing Results on the Wiki page for adhesives, but am still lost.
The original vitrine joins have partially separated, and some of the resulting gaps have a flat ribbon-like adhesive that zig zags between the sheeting. I do not have access to the original build specifications, and am unsure as to how to figure out what was originally used. I know I do not want to cross-link any material, and I definitely do not want to cause damage to any specimen that might be displayed in the future. Will I need to test the "ribbon" adhesive? If so, how? Any help or direction would be greatly appreciated.
Link to post: https://community.culturalheritage.org/discussion/vitrine-repair-1?ReturnUrl=%2fcommunities%2fcommunity-home%2fdigestviewer%3fcommunitykey%3defc8a209-1e74-4c1b-80d7-cb26db836184
You are welcome to respond through me, directly to her (heidi.mead@gcsu.edu), or in the community (https://community.culturalheritage.org/home). Any information you can provide would be greatly appreciated.
Sharon Fickeissen
Connecting to Collections Care Monitor
Senior Conservation Technician
Hagley Museum & Library
sfickeissen@hagley.org
------------------------------
Sharon Fickeissen
Connecting to Collections Care Monitor
Senior Library Conservation Technician
Hagley Museum & Library
Wilmington DE
sfickeissen@hagley.org------------------------------
Original Message:
Sent: 12-01-2022 10:54
From: Heidi Mead
Subject: Vitrine repair
I am interested in attempting to repair vitrines that would exhibit natural history specimens. Does anyone have any recommendations for working with acrylic sheeting, adhesives, and museum specimens? I would prefer to work with materials and methods that are conservation approved, I just don't know where to look to find them! I poked around in the Materials Testing Results on the Wiki page for adhesives, but am still lost.
The original vitrine joins have partially separated, and some of the resulting gaps have a flat ribbon-like adhesive that zig zags between the sheeting. I do not have access to the original build specifications, and am unsure as to how to figure out what was originally used. I know I do not want to cross-link any material, and I definitely do not want to cause damage to any specimen that might be displayed in the future. Will I need to test the "ribbon" adhesive? If so, how? Any help or direction would be greatly appreciated.
Thank you all,
Heidi Mead
------------------------------
Heidi Mead (she, her)
Vertebrate Fossil Preparator
William P. Wall Museum of Natural History
Georgia College
Milledgeville GA 31061
------------------------------