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How to Etch them

Copyright Dec. 2005
Lynn Mills
All rights reserved

Bountiful High, Utah, class of 58.

The fossils this article is about are from Northern and central Utah. The ability to etch these fossils very from one specimen to another and I have no knowledge of how well fossils from other geographical areas will etch. The fossil bearing rocks from northern and central Utah were limestone or a mixture of limestone and sandstone. I found that rocks containing large amounts of sand mixed in with the limestone were much harder to etch than the pure limestone. The difficulty to etch the limestone was proportionally harder as the sand content increased.

     Watching a fossil slowly emerge from the darkness of a stones interior into the daylight after being hidden for eons is almost a spiritual experience. You are freeing a fossilized animal from its stone walled dungeon where it was imprisoned for perhaps millions of years. Finally they are able to bathe in the light of day for the first time in a long long time. Here is the method I use to etch fossils.

     Lime stone can be dissolved using Muriatic acid, (Hydrochloric acid). This is not to be used by children and of course eye protection is a must. It would be a good idea to keep a concentrated solution of baking soda on hand to neutralize any accidental exposures or spills. Work in a well ventilated area and avoid breathing the fumes. A set up like the one shown below is ideal. If you don't have access to a burette and if you are handy it is not very difficult to rig  a simple dripper with a plastic funnel, some fish aquarium tubing that tightly fits the small orifice of the funnel and a pair of clamps to control the drip rate by pinching the tubing.


Etching Fosils

Some Lime stone samples dissolved faster than others.  By using a burette set up like the one shown on the left it allows you to adjust the drip rate for fast or slow dissolved lime stone. As the lime stone dissolved in one spot you can move the  specimen to selectively dissolve the desired areas to bring out the fossil in the best relief possible. To get the finer details you can use a Q tip dipped into the acid to slowly bring out finer details that would other wise be lost. An average drip rate is about one drop of acid every five seconds.

Be sure to put an acid proof plastic tray under the sample to catch the acid overflow.

Before etching

It just looks like a plain piece of rock but under the surface are dozens of fossil remains waiting to tell their story.. As the Muriatic acid begins to drip ancient animals begin to appear.

After etching

After several hours of etching this is what emerged. The black lime stone etches rapidly but the fossils are dissolved too at a slower rate so care must be taken not to go too far. I am not sure if this is a snail or ammonite. If some one knows please email me.

Horn coral

A horn coral is exposed in this etched  sample. These fossils came from a 9,000 foot elevation about twenty miles North East of Logan Utah  yet when these fossils were alive they were living in the bottom of the ocean. This piece of Lime Stone contains snails, Ammonites, gastropods, Crinoids, horn coral and honey comb coral, (not visible in this picture) and unidentified broken bits and pieces. A interesting thing that I have observed is that frequently the fossilized clam shells are tightly closed. To me this indicates a catastrophic event that hopelessly buried the clams alive. Possibly under tons of volcanic ash or pyroclastic flow debris. As you walk the beaches and see clams that have been dead for any length of time they will naturally be wide open. and as the flesh holding the halves together degrades the two halves separate and are scattered. If the fossilization took place over a millennial the halves would have been scattered long before the fossilization process

Knee joint

This fossilized bone was found on private property in the west end of  the Salt Lake Valley on the East face of the Oquirrh Mountains about 5000 feet above sea level. It is a knee joint and was partially encased in Lime Stone. The blue area is where the femur was broken off. The red dot is where the ligament hooked on. The green dot is an entrance for a blood vessel. The yellow is the cartilage area. A person at the museum at the University of Utah was unable to identify it but it is obviously from a vertebrate. Some of the lime Stone was intentionally left on the back side of the fossil and contains fossilized sea shells. I will leave it to you to draw your own conclusions as to what this means.

Jaw bone

The following pictures are not etched samples and are placed just for the readers benefit and enjoyment.

     This is a petrified jaw bone with two empty tooth sockets and one tooth still in place. While panning for gold in a creek bed, I found it in my gold pan in the Puget Sound area of Washington state. I have no idea what animal it came from.

Iron pyrite shell

     This is one of the few fossils I have purchased. It was purchased here in Bremerton, WA. at a rock,  gem and mineral show. It is iron pyrite, fools gold. I have no idea what the process was that formed this or how common Iron Pyrite fossils are.

Trilobite in shale

     This is a trilobite My daughter found while we were fossil hunting in Juab County in central Utah. It is  in shale and is not etchable. To find the trilobites you have to split the layers of shale till you find a good specimen. The object on the right side of the picture is just an imprint left by a Trilobite fossil that fell out of the shale when it was split open. On the left is a trilobite still in the shale.

Evidence of a tsunami?      Almost fossilized! This is a piece of wood from a layer of debris that has been exposed in the side of a cliff near Port Angeles WA. It has been severely compressed by the weight of the mountain of earth that sits on top of it. Is is so dense that it will no longer float and if you tap on it it almost rings. The shiny area is where I sanded it and polished it. Where it has been polished it looks and feels just like Ebony and is probably just as hard.  
Once round limb is now flattened.      This is the above piece of tree, or tree limb on it's side. There is bark on both sides so what was once a round tree or limb was flattened by the immense weight of the earth piled on top of it. The debris layer is a couple of feet above the water line of the Straight of San Juan De Fuca and probably represents debris, trees and limbs that were buried by a head on collision with a tsunami racing into the Straight of San Juan De Fuca and into Puget Sound. Sea shells in the overburden one to two hundred feet  above the debris layer is further evidence of a tsunami. Neither the wood in the layer or the sea shells above the layer of trees and limbs are petrified which indicates a very recent event geologically speaking. 
Oklahoma Rose Rock.      Though this is not a fossil I am putting this on the page just as a matter of interest. It is a rose rock from Oklahoma, near Oklahoma City. It is composed of 50% sandstone and 50% Barium. The Barium is responsible for the rose petal shapes and makes it very heavy It is the same stuff they make you to drink, Barium Milk Shake, when the doctor refers you for a GI exam.  

I hope you enjoyed  the page. I am not an expert on fossils so if you have more information to add or corrections I would enjoy hearing from you.
Email Lynn.