How do you know that cold is a threat to ceramics?
Fact: Extreme cold makes standard ceramics more brittle. Silica ceramic space shuttle tiles are not in discussion, here. Our typical ceramics, going from room temp to freezing contact (such as in snow, or a cold stream), are at risk for breakage. I know it's pretty to photograph ceramic models in streams and lakes, but there is an inherent risk. There is also the problem of a hollow body, full of warm room-temp air, and those thin legs, now deep in snow... There is a temperature differential between body & legs that can't be good. I've heard of a ceramic horse that shattered its body on impact with snow. Cold is not a friend.
What is thermal shock?
When hot or cold meets a room temp (or more extreme) item, the resulting spontaneous damage is from the thermal shock.
Picture the ceramic horse as not only a big, hollow body with solid-poured, delicate legs, but the clay and glaze each have layers, bonds, and weaknesses inside them, due to salts, hard minerals, how much water was used to seam them after drying, and the temperature at which they were first bisqued.
Now picture this horse, with all of its many variables, some intrinsic and some acquired, full of air at any temp, and then expose just its surface area to a temperature extreme from that inner temp. Or how about just its legs? Maybe a soak of cold rain or sleet?
Thermal shock makes the bad stuff happen right where the materials host these temperature and humidity extremes. The bad stuff is dunting, shattering, shivering, and shock-caused (not age-related) glaze crackle.
Nothing good comes of this, unless, of course, you are doing a raku. Even then, there is planning, and things still can explode.
Earthenware is the most susceptible, although stoneware, porcelain and bone china also can be damaged by extremes. A home dishwasher is a micro-climate extreme example. The Victoria & Albert Museum site puts it succinctly:
"Do not use a dishwasher to clean valued ceramics. High temperatures, high pressure water and aggressive detergents can permanently damage glazes and coloured enamel decoration."
What if it is a hot summer? How do you know that ceramics that came in from hot outdoor temperatures are safe to unpack in an air-conditioned home?
Because my kiln says so. "Unload kiln when temperature [of the kiln interior] falls below 130˚F." Just above this, it says the kiln must not be used where it exceeds 100˚F, so it is assumed that some kind of climate control is in use around this model of kiln. The 100˚F limit is intended to protect the KilnMaster computer.
There is little chance that deliveries will be made on a day where your local outdoor temperature is 130˚F, so don't sweat it. The big trailers, that carry parcels to distribution centers, are said to reach 130˚F inside. Most people do not receive a box direct from a tractor-trailer at their doorstep, and usually hours have passed since that exposure.
Now, if your item has known restorations, and was shipped through extremely hot or humid weather (including the weather at carrier hubs, where it sat on sizzling tarmac) that is probably bad news, whether you open it sooner or later.
What is the most heat-retaining package material?
To put it simply, Air. The more closed bubbles of it, the more it holds the temperature at which it was packed.
Styrofoam and egg crate foam are the winners in this. Bear in mind, for summer shipping, egg crate heats up fast and holds that warmth. Cold-painted (including restored areas of chinas) will want to stick to it, if heated.
I don't recommend shipping with a heat pack, because the one pack means heat on one side, and cold on the outer extremities. Even if the warmth is retained in foam, it only lasts about 6-12 hours. This is why live animals are shipped by overnight 10am delivery, or faster.
The package insurance covers any breakage if the box got too cold in transit, right?
Only if you also inquired and bought that carrier's Freeze Damage insurance policy, which is a whole separate fee from normal insurance coverage. The USPS, for instance, does not cover damage from freezing nor overheating in transit, even if you bought their regular insurance.
What is the usual method of unpacking cold boxes?
There are a few variations on a theme of Wait. When the box is handed to me by the carrier, I carefully set it down near a space heater and don't touch it until it's warmed up.
Knowing how outer boxes insulate, I will sometimes cut open the tape on the outer box only, arrange the flaps open, and sweep any styrofoam peanuts off the top of the inner box. I don't move the boxes, at all. Now, room temp air can touch the outside top of the inner box.
If the boxes weren't terribly cold, and the inner box feels room temp, I can open it at the end of the day. Sometimes, I don't open it for 24 hours.
Why do you tape the open edges and the seam of boxes, not just the long, middle closure?
Because when a box travels through various hubs, it may be exposed to humidity, rain, snow, leakage from other boxes. Even just a simple edge taping can reduce the risk of box failure. I have had soaked boxes arrive that were only held together by the extra edge tape. They resembled the sagging Halloween pumpkins of mid-November. Not only does this tape help guard against the loss of the box's integrity during storms, but it prevents that super-cold moisture from seeping into the packing that touches the ceramic horse. Icy water suddenly soaking a room-temp, insulated ceramic induces temperature shock, too.
Cold or warm, shipping tape hates humidity!
Now that I have thoroughly horrified you with some risks to shipping in extreme weather, I will share one little story.
A sudden snow storm came up here, while I was anticipating the arrival of an (earthenware) vintage Hagen-Renaker large Zara. The shipper had done a fine job, but the postal online tracking system, the day before she was due to arrive, completely lost her. When my mail arrived that afternoon, no Zara, the post office itself had closed to the public for the day. Snow had upset the normal carrier schedules. A phone call to the PO, now after hours, and they said they'd take a look in back, but it wasn't on the computer (no kidding). When they had found it, they called and instructed me to pick it up right then, since the staff were still working in the back. The snow was coming down thick, and my husband drove us there. At the back door, I received a wet box that was positively freezing. It felt like it had been sitting outside in the snow storm, on the loading dock, for hours. It looked like it had been dropped a few times, too.
I got into the car with dashed hopes. There was no way this survived. The only comfort was that I knew the Zara already had some damage. I waited an hour, with the box by a space heater, and figured the shock damage was done- why wait any longer?
Thanks to the seller's packing, she was fine. Ice cold to the touch, and I let her rest in her packing a while longer, but no new damage.
Take a little extra time with your winter arrivals, and always ship something the way you'd like to receive it. Stay warm, and enjoy your new additions!