Does anyone actually know the recommended amount of weight not to exceed on glass shelves inside curios? Is there a formula that can be utilized re length, width, and thickness of glass? I'm sure many of us might be tempted to put too many HLs on a shelf which could be hazardous to our collections. Any engineers out there that can explain the area of square inches not to exceed when displaying HLs on glass shelves?

Boy Bob, you have asked a tough one. Hope someone else has the expertise to answer better than I have...

As an Architect I deal with quite a few structural engineers, but most are not trained in the structural capabilities of glazing. With an almost infinate list of glazing materials: sheet, float, plate, rough plate, tempered, annealed, heat strengthened, spandrel, laminated, wired, etc. as well as various grades of quality of each, most engineers stay away from structural responsibilites of glass. Many engineers would therefore in any special circumstance just specify required loading conditions in the construction specs for the glazing manufacturer to meet and take responsibility for. ie: "I'm not going to be responsible for that...that's your job".

Since this question is not a major construction project you will not receive any accurate calculations from a manufacturer or "generic" loading tables that are easily interpreted (unless your NASA or I.M. Pei, etc). I have never personally seen any standardized loading charts for horizontal plate glass. The quality of the glass and specific manufacturer has a large impact on an accurate calculation. If you talk to most glazing companies, they will probably just give you some general common sense approaches to your concerns, which would apply to the curios.

SUPPORTS:
In many curio loading conditions, the end supports will more than likely be the critical structural aspect of the shelf. Are they plastic? metal? 2 per end? 3 per end? a continous support (wood ribbon strip)? or just the small "pegs"?
The optimum support would be a continuous ribbon support around 3 sides. Most curios have a mirror in the rear, so rear supports are not possible. If only supported at ends, replace the clear plastic L-shaped "peg" type supports with metal ones. The plastic could shear off with a substantial load (depending on the design of them), especially if loosely fit. Make sure the support pegs are snug and fairly deep into the side of the cabinet also. A continuous rear support will *greatly* enhance the amount of loading allowed to the shelf and is probably the single best "easy" solution when available.

GLASS TYPE AND THICKNESS
Plate glass is the most common glass for curios. Tempered or heat strengthened glass is approx. 2 to 6 times stronger than plate glass, but only in a vertical condition. Replacing the plate glass with the others is really not going to help you much in a horizontal loading condition. Of course if the shelf fails, tempered glass won't break into large chards which possibly could save a sculpture or 2...but doubtful since the lightest bump can break the sculptures.
The single most important "self assurance" you can have in your curio is to increase the plate glass thickness. If your existing shelves are 1/4" plate, I would suggest increasing to 3/8" (or even 1/2") if the unsupported span is much more than 3 feet and unsupported at the rear (but only if your trying to cram them in and your willing to spend the money to be "extra safe"). The cost of upgrading the glass is probably a smart investment if you have a CH1, Coquille, Portland Head, etc. Clear spans 30" or less seem to hold up fairly well with 1/4" plate if you at least spread the sculptures a little and keep "Navesinks" off them. A 16" x 30" end supported 1/4" plate shelf seems to hold 10-12 average size sculptures fairly safely, but I would not cram them much tighter.

My personal suggestion would be to modify the shelf supports as best as your curio permits, and increase the glass thickness a little. If you are a very creative person, buy an extra piece of glass of same exact size, material, and support locations as your curio. Take it out to the shed and carefully start loading it with some weights until it shatters. Then never load your curio more than 60% of the critical load. It's fun being destructive occasionally!

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-RodW
[This message has been edited by Rod Watson (edited 12-22-98).]

But of course, NOT your Harbour Lights

>>If your existing shelves are 1/4" plate, I would suggest increasing to 3/8" (or even 1/2") if the span is much more than 3 feet and unsupported at the rear (but only if your trying to cram them in and your willing to
spend the money to be "extra safe").<<

Thanks for a very informative post, Rod. I'm clueless about structural properties, but the following remarks come from personal experience:

If you're getting custom glass made for a cabinet, you might want to get the edges beveled or rounded. A square edge can cause more damage if you accidently bump a piece on it, and is itself more susceptible to knicks and chips.

Also consider the weight of the glass itself - thick glass can get heavy! With 3/8" - 1/2" thickness you could end up reducing the integrity of your mounting system because of a significant increase in weight. Especially with small diameter mounting pegs held in wood.

I'll temper these remarks by noting its clear that decent custom glass is expensive! Don't glaze over the need to insure safe transport. If you're picking up from a shop. bring plenty of blankets to avoid a paneful ride home.

Shattered,
__
/im [Exile on Fog Street]

Whatever you do, please be VERY careful. If you want to see something that would make any grown man (or woman) cry, buy the current issue of Collector's Mart magazine.

There is a column in there that talks about insuring your collectibles and as a rather harsh example tells the tale of an older gentleman who had just sat down to a nice breakfast one morning. He suddenly heard a loud CRASH! He ran into the living room to see his cleaning lady frozen in front of his curio cabinet. He had a collection of Hummels that had taken he and his recently deceased wife a lifetime to collect together. Many of these were in pieces on the floor.

To add extreme insult to his injuries, he was informed that his household insurance policy would not cover any of his loss.

Are you ready for this???

He had to eat the loss of Hummels with a book value of $28,000!

So my advice is two-fold. If you have a sizeable collection of Harbour Lights, Hummels, or anything else, insure them with a company that specializes in insuring collectibles. And when it comes to displaying your collectibles, don't be a cheapskate. If you run out of room, pack them away or get another curio cabinet. Curios are expensive, but not as expensive as replacing part of your collection.

You guys are a wealth of information! I hope I'm not going to be billed for this...it could cut into my HL budget!

My new curio is going to be delivered on December 28. Both my current and new curio have 3/8" glass shelves. I know the older one is quality construction. The newer one is made by the same company and for $1800 it too should be a quality piece. The newer one is wider than my original and that's why I was a little curious about how much weight it might hold. I certainly wouldn't want to experience a "crash." I'll definitely keep Navesink on the bottom. Thanks for the info.

Excellent posts, all, especially Rod's. I've been seeking answers to the same questions concerning the amount of weight that glass shelves can support. Not even the glass company that I bought them from could provide a decent answer. My personal experience (so far) has been good with ten 37 X 12 X 3/8 inch shelves. They're supported at each end by two L-shaped metal supports. I've loaded one or two with as many as 12 HL's of varying sizes with no failures, although the average # of pieces per shelf is closer to 8. I've never used 1/4 inch glass and never even considered it - it just LOOKS too thin!!
Thanks again, Rod, for an excellent treatise!! :>)

If you don't mind, who makes the curio, Bob?

__
/im

Well guys, guess what I'll be doing when I'm through here?
Yep, rearranging my HLs in my largest curio.
The shelves measure 44" long...they're 3/8" thick. The entire front
is glass. Including the bottom, there are 5 shelves. The 3rd shelf
down has a strip of wood that the shelf rests on. The other 3 shelves
only have 2 metal rests on each end to support the glass. My thanks to
Rod for his pointing out to us the dangers that the support system can create.
It's one aspect that my husband and I failed to consider when we purchased
this curio.
I thank you.....My insurance company thanks you.

Debbie


[This message has been edited by tnkeeper (edited 12-22-98).]

I purchased my first curio from Thomasville Furniture. I don't know if Thomasville is known nationwide, but it's an upscale furniture line. Even the sales personnel are upscale. When I shopped around for my second curio, I went to Thomasville and found they had raised the price of mine by $110. They say they have minimum retail pricing or they lose the line. They wouldn't budge on the price so I decided to shop around before I made my purchase.

I kept looking around and found an excellent curio at one of my local furniture stores. While looking through their book I found out that my Thomasville curio was made by this same company. The company's name is Jaspar. It has all the features of a great cabinet. I especially like the workmanship, 3/8" glass shelves, and full piano style hinges from top to bottom on both doors. When you open and close the doors the cabinet does not "rattle". It feels real solid. It was the most expensive curio I looked at but the quality won me right over. Remember: "The quality lives on long after the price is forgotten."

That's the word from the East Coast!

When we first acquired a curio cabinet (by Pulaski) for our Harbour Lights, we purchased a 55" wide cabinet that had 1/4" thick tempered glass shelves (44" wide by 12" deep) with only metal supports at each end. We managed to get the glass shelves replaced (by the manufacturer) with 3/8" shelving. After loading the cabinet shelves, we stepped back to admire our handiwork, only to notice the shelves were "sagging" (followed by a frantic removal of all of the lighthouses). After many calls and discussions with the retailer, manufacturer, glassmakers, etc., all would only safely guarantee 10 lbs per shelf (which was a waste of shelf space). After further calls and discussions of various ways and means for safely getting more than 10 lbs. on each shelf, we came up with a solution to our problem which has worked extremely well. We purchased an acrylic rod (approximate diameter of a 25 cent piece) which we had cut to precise measurements to fit between each of the shelves and spaced exactly in the middle (front to back and side to side). The shelves were removed and then replaced (one-by-one) with the acrylic rod held in place with a drop of (removable) adhesive placed on each end of each rod. We allowed 24 hours for the adhesive to "set-up" before loading the lighthouses. We now have approximately 25 lbs on each shelf and have not had any problems (for the past two years). Since the rod is clear/transparent, it is barely noticeable and many visitors didn't see it until we brought it to their attention. It does take a lot of patience to get the measurements, have the rod cut to the exact size(s) and position the rods directly on top of each other between the shelves (one -by-one). In retrospect, the added peace of mind has been well worth all of the trouble and efforts - and the cost was nominal.

As to the weight of each lighthouse, we use a kitchen scale that can weigh up to 4 1/2 lbs (used for all but Navesink). Navesink is ALWAYS on the botton shelf!!

Hope this helps others with this concern.

I am a Glazing contractor and glass is stronger than alot of people think. Most people would never think of walking on an atrium, but I have done it ( DO NOT TRY THIS AT HOME AS I AM A PROFFESIONAL). The span (distance between supports) is the key. However as you load glass, it becomes more stressed and less likley to withstand a blow. as for the problem of lack of back supports due to glass or mirror, you can get a clear silicone and caulk the underneath of the shelf to the glass or mirrored back. Be sure it is a structural glazing though, for strength. Look in your yellow pages under construction materials or call a Glazing or Window Contractor in your area for availability.

Hi Luvlights...got a couple of questions for you...Is glass the same strength on both sides? That sounds a little weird but I was wondering about the groove etched in on one side for displaying plates. Does it make any difference in load capacity if that groove is facing up or down? Also does it make any difference on where you place the HLs on the shelves? I usually try to put the heavier ones near the corners that are supported by the metal tabs. Does it make any difference?