nd.gov - The Official Portal for North Dakota State Government
North Dakota: Legendary. Follow the trail of legends

Backstage Pass to North Dakota History

This blog takes you behind the scenes of the State Historical Society of North Dakota. Get a glimpse at a day-in-the-life of the staff, volunteers, and partners who make it all possible. Discover what it takes to preserve North Dakota’s natural and cultural history. We encourage dialogue, questions, and comments!

Becky Barnes's blog

The Art of Making Fossil Casts

A few blogs ago, I introduced the good kind of mold we have in paleontology: silicone rubber, used when making casts of fossils. Depending on the purpose of making a cast, the end result can look very different. If we need to make a cast to replace an original fossil, a lot of time and care are taken to paint the cast to make it look as close to the original as possible. If a cast is meant to be a teaching tool, handled frequently, or given away as a prize, then maybe a more generic paint job (i.e. less time) is used.

There are times when people are conflicted – they found a cool fossil, and they want to donate it to the State Fossil Collection, but they would also like to keep it to show their friends and family. Depending on the fossil, we can make a cast and paint it to match the original. This way the person can keep what looks (and even weighs) the same as the original, but the real one is safe in collections.

Mosasaur vertebra casts and original fossil

Two painted casts of a mosasaur vertebra, and the original. Which is which?

During our 2017 dig season, our public diggers came across two beautiful Tyrannosaurus teeth. Everyone wanted the teeth – yet there is only one of each. What to do? Make copies and paint as close to the original as possible. After making a silicone mold, it was time for an assembly line. There is no point to mixing up all the paint you need, over and over, to paint one tooth at a time. So we cast a bunch, mixed our paint, and started the lengthy process. In order to keep all the surface texture, the paint had to be applied in thin layers. Wash after wash. While it is nearly impossible to match a tooth exactly, we can get close enough. This means lots of small brushes, and patience.

One of the failings of casts is that they are often much lighter than their rock counterparts. To fix this we weighed the original tooth (171 grams). When mixing our plastic (~65 grams), we made up the difference in weight by adding metal BBs without adding a lot of volume.

T. rex teeth on scales

Original Tyrannosaurus tooth (left) and 80 percent painted cast (right). Weight distribution in both teeth is the same.

We can’t just let the plastic and BBs sit in the mold, or all of the weight would be on one side. So, we have to rotate the mold until our plastic sets. Time consuming? Yes. Great arm workout? Yes. Awesome teeth? Totally.

Becky turning box

Becky becoming the human gyroscope. Turn, turn, rotate, pivot.

Mastodon Repair

Museum staff often have to walk a fine line when it comes to displays. Sometimes we get it right, and other times a little modification may be needed. If barriers are put up (such as Plexiglass, metal railings, etc.), some people feel offended or think that we’re trying to keep them away from the object on display. However, if we have no barriers, sometimes people get a little…too…up close with the artifact or specimen.

One of our first priorities is to keep the object on display safe. Without them, there is no museum! A gallery filled with photographs of fossils isn’t the same as seeing the real thing. Safe for the fossil? Yes. Good for museum patrons? Not so much. Another priority is to keep our museum visitors safe. For the most part in this state, we see a good dose of “North Dakota Nice,” which helps us keep our barriers to a minimum and objects close for viewing. There is the occasional mishap however.

Mastodon repair wrapped up with bandaid sticker on it

Plastic shrink-wrap and a touch of humor to hold the bones in place while the glue dries.

Someone trips over untied shoelaces, and bumps into a painting. Perhaps you wish to show everyone where you are, and during a selfie opportunity lean too far back, knocking into a display case. Or maybe an over-exuberant child who has escaped the watchful eye of parents runs into the leg of a Mastodon.

Becky Barnes lying down to paint the mastodon repair.

Not all repairs are conveniently placed! Becky touching up some spots of plaster with brown paint.

This last case did happen. No one was hurt, but the Mastodon legs did suffer some…dislocation. So what happened then? We fixed it. After making sure the bone was still in good condition, we looked for what went wrong with the display mount and how to counter the problem in the future. The radius (lower arm bone) was previously only glued into place. To repair it the bone was first cleaned, then we re-glued the bone and added some wire support. The wire was painted brown to match the bone and make it less distracting than shiny silver. To give the bone a little extra support while the glue was drying, we added a temporary layer of shrink-wrap.

Becky painting the mastodon repair

Becky concentrating on painting the newly installed silver wire.

The physical railing around the Mastodon is very low, so it doesn’t distract from the skeleton itself. There’s not a whole lot of modification that can be done on that aspect. So – can people touch it? Even though the physical opportunity is there, the museum staff sincerely hopes you will use photo opportunities, rather than tactile ones. Help keep our museum safe – safe for you and safe for the specimens and artifacts – and enjoy North Dakota’s history!