An experiment in fossil preparation by Richard Forrest

By January 3, 2019Uncategorized

For those of you who know Stamford and District Geological Society member Richard Forrest and his canny habit of not to be beaten by the fossil in front of him when it comes to prepping.

Well here is another example of one his tried and tested techniques on the sea urchin a Clypeus ploti. 

Field Secretary Kenny Nye has been very busy over the past couple of months fine tuning the society’s field trip calendar for 2019. With some potential dates pencilled in for Ketton Quarry so perhaps we all can try Richards technique quoted below 😊  

“If like me you collect fossils, you may have been struck by the way in which natural weathering can ‘prepare’ fossils rather better than standard preparation methods. This intrigues me, and has made me wonder if this can be replicated in some way. My best guess is that the natural process is a combination of freeze/thaw cycles and mildly acid washes from rain. So this is my kitchen sink (rather literally!) experiment. I’ve used two echinoids of the genus Clypeus collected from the Blisworth Sandstone from Ketton as test subjects. These fossils are relatively common, and no great loss if the experiment destroys them. Both were partly covered by hard matrix when found. I first soaked the specimen in water made slightly acidic by a slug of vinegar. After leaving it for a couple of hours, I drained away the water and put it in the freezer at a temperature of approximately -20˚C. After a few hours, out of the freezer. To start with I then poured warm water over specimen. After the first few cycles I used boiling water. The initial effect of this was to spall small fragments of matrix off the surface.”

Fig 1: Above is specimen 1 after 4 cycles – dorsal view. Some matrix has come off, but there is a long way to go! At this stage I was scrubbing the echinoid with a toothbrush after it had cooled.

Fig 2: Above is specimen 1 after 4 cycles – ventral view.

Fig 3: Above is specimen 1 after 10 cycles – dorsal view. More of the matrix has come off, but it’s a slow process. I started to use some mechanical assistance at this point, pinging off matrix using a penknife.

Fig 4: Specimen 1 after 14 cycles – dorsal view. Most of the matrix has come off, either by spalling off as the boiling water hits, or by pinging off.
Fig 5: Above is specimen 1 after 18 cycles – dorsal view. The last few cycles made little difference, so this is about as far as the process can go.

Fig 6: Above is specimen 1 after 18 cycles – ventral view.

“The process seemed to work pretty well. I started a second echinoid when part-way through the process making use of what I had learned at the time. The freeze/thaw cycles spall off small fragments of matrix as a the hot water hits the specimen and expose fine surface detail which other methods may not reveal. Larger, hard chunks of matrix are softened and can be scraped off more easily. This is a very limited experiment as only one type of fossil from one Formation was used. Many fossils are affected by water, and obviously cannot be prepared in this way. Fragile specimens may disintegrate under the thermal stresses created. But then, as every experienced preparator knows, each fossil is different, and needs different preparation methods. Specimen 1 has been given to my grandson Otis who was born on the day I found it – you need to start them young! The following images are of the second specimen and show the fine surface detail the process has revealed.”

Fig 7: Above is specimen 2 fully prepared – dorsal view. Some fragments of matrix are still there on the surface, but it is better to stop subjecting the specimen to thermal stress rather than tryng to attain perfection.

Fig 8: Above is specimen 2 detail.

Fig 9: Above is specimen 2 detail.

Fig 10: Above is specimen 2 detail.

“Photographs taken on Olympus TG-4 using integral focus stacking and LED light guide.”

So these are the ‘pound stones’ William Smith was finding in the story of the first geological map – The Map That Changed the World’. It’s a nice little historical footnote for these great specimens.

Thank you Richard for sharing. 

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