Freeze-dried pickles?

reduced tapewormsProducing a traveling exhibit has its own set of challenges, the biggest being that it travels! Set-up and tear down have to be easy, the components have to be crated and shipped, and the specimens have to be hardy. This leaves a big challenge for preserved wet collections – or pickled specimens as they are often called. The fluids used to preserve specimens require special treatment in shipping and including them in a traveling exhibit make for a very complicated shipping process. On the other hand, leaving them out means leaving out some of the most interesting specimens and losing some very powerful visitor experiences. So what to do?

Judith Price, Assistant Collections Manager for the invertebrate collection at the Canadian Museum of Nature may have found an answer. Recently she experimented with freeze drying some of the preserved wet specimens. The results were incredible. Despite a lack of colour from the pickling, the detail of specimen’s texture was amazing.

Here’s Judith’s explanation of what was done.

Most invertebrate specimens stored in scientific collections are “pickled” in alcohol or other fluids to preserve them for study. Unfortunately these fluids are usually flammable, so the fire department sets safety limits on how much we can use in a public space like our new Water gallery and traveling exhibit. We decided to try freeze drying some specimens to see if that would be a better way of exhibiting the diversity of aquatic life. Since preserved animals lose all the colours they display when alive and are left a dull pink, this would also let us tint the specimens to look more lifelike, and use them in dioramas.

Our freeze drier is mainly used by the researchers who study diatoms, single-celled plants with a shell made of silica. Paul Hamilton, one of our botanists, showed Jean-Marc Gagnon and I how to use the machine (which he thinks is simple but I beg to differ!)

For our first run, Jean-Marc selected from our collections a few invertebrates of various sizes and fragility: some small to medium sized crustaceans (the group that includes lobsters and crabs), a marine worm called a “blood worm”, a couple of small sea stars and two small sea cucumbers with their mouth parts exposed. These last are very fine and almost frilly, a good test of the stability of softer tissues.

We pinned the softer animals in a glass dish with wax in the bottom, then submerged them in water. This was intended to support them and to reduce surface shrinkage. Then into the freeze drier they went!

The freeze drier works by pumping out as much air as possible from a well-sealed container, allowing the water to more easily escape from the specimens inside. The air is then passed through a very cold chamber where the water vapour collects as an ice block so we can remove it later.

We made one miscalculation: the water around our specimens didn’t freeze as a block, it bubbled and boiled and when it finally froze it looked like a pile of snow! This is because as the air pressure lowered, so did the boiling point of the water (this happens as you go up in altitude for the same reason). Next time we will use a regular freezer to stabilize the samples before putting them in the freeze drier.

Although we had a scary day before the “snow” evaporated off the specimens, the experiment turned out very well. All the animals came through wonderfully, although not with “flying colours”. Our exhibit specialists will paint those back on before these specimens go into our new galleries!

These delicate little specimens can now be painted to reflect the natural colour. A few more experiments and the traveling exhibit may have its specimens after all!

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