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Long-term effects of shellac?


errant.beasty

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I've heard that shellac is not commonly used to coat fossils and bones anymore because it doesn't hold up well over time. Does anyone know how long it typically takes for shellac to start darkening and cracking? Do you have an alternative you prefer?

 

Thanks!

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I’m very bad at actually starting projects, but I’ve been meaning to use some butvar to coat some stuff (which I heard works great.) Paraloid works great as well (or so they say)

“...whilst this planet has gone cycling on according to the fixed law of gravity, from so simple a beginning endless forms most beautiful and most wonderful have been and are being evolved.” ~ Charles Darwin

Happy hunting,

Mason

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Shellac will turn a bit yellower over time and it will start to crack.  There are some really good polymers out there that you can use.  Like Whodaman has said, butvar and paraloid and a couple other should work purty good. 

 

RB

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4 hours ago, errant.beasty said:

Does anyone know how long it typically takes for shellac to start darkening and cracking?

Depends on the environment it is in. If it is kept in a temperature controlled and dark conditions it can last for a long time, if it is exposed to light and moisture it can decay much quicker.

Darwin said: " Man sprang from monkeys."

Will Rogers said: " Some of them didn't spring far enough."

 

My Fossil collection - My Mineral collection

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4 hours ago, errant.beasty said:

I've heard that shellac is not commonly used to coat fossils and bones anymore because it doesn't hold up well over time. Does anyone know how long it typically takes for shellac to start darkening and cracking? Do you have an alternative you prefer?

 

Thanks!

 

Yes, I've heard that too but I have a couple of crab impressions (Pinnixa galliheri) that I coated with clear shellac at least 20 years ago but they still look fine - no cracking or darkening.  Clear shellac actually helps darken some fossils a bit when first applied - great for fossils that have some detail but are about the same color as their light-colored matrix.  I think any colored shellac would at least darken or discolor in a way you don't want.  Of course, it might depend on how your fossils are stored (boxed in a room without a wide range of humidity and temperature changes or less-enclosed in a garage or poorly-insulated outbuilding.

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On 2/18/2018 at 9:48 AM, errant.beasty said:

I've heard that shellac is not commonly used to coat fossils and bones anymore because it doesn't hold up well over time. Does anyone know how long it typically takes for shellac to start darkening and cracking? Do you have an alternative you prefer?

 

Thanks!

When I was at the Tucson Fossil Show a few weeks ago I bought a Merycoidodon skull that was found in the 1920’s and coated with shellac at that time.  While it looks like it may have darkened very slightly with age, I don’t see any cracking or other signs of deterioration.  In fact, even before I knew its history I was attracted by its overall appearance compared to the other more recently collected skulls.  It stayed in South Dakota all that time which is probably not the same as if it were in a more humid environment.

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Another thing that shellac supposedly does is that it never really dries out, so over the decades it actually collects micro-dust articles. 

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Have used polyvinyl acetate a couple or few times, no complaints so far. Iirc the only concern was it becoming more fragile in cold conditions but that's not a concern where they're stored; more inexpensive than butvar too

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Shellac was used in 19th century photography (my professional field) and does yellow and crack over time. Victorian era photographers used oils to give a little flexibility preventing the cracking or crazy paving effect. These varnishes were used to protect images on glass and metal to prevent tarnishing (chemical damage) and physical damage. The oil normally used was lavender oil which certainly now can be quite expensive. I have used other oils and not noticed any detrimental effect over several years of exposure to extreme UV light/radiation in order to advance more natural UV radiation i.e. the sun. 

 

A more typical 19th C photography varnish in photography used gum sandarac dissolved in ethanol with the addition of lavender oil (for the same reason as above). 

 

As an exercise it would be interesting to see how hum sandarac varnish would work on fossils. It is reversible as ethanol can be used to remove the varnish in my he same way as acetone can be used to remove Paraloid and similar products. 

 

The photographic method that used this varnish is called wet plate collodion. Plates made on glass are called ambrotypes and on metal tintypes (in the USA) not that they were ever made on tin (Sn) or ferrotypes this side of the pond. 

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On 2/26/2018 at 7:51 AM, Sagebrush Steve said:

When I was at the Tucson Fossil Show a few weeks ago I bought a Merycoidodon skull that was found in the 1920’s and coated with shellac at that time.  While it looks like it may have darkened very slightly with age, I don’t see any cracking or other signs of deterioration.  In fact, even before I knew its history I was attracted by its overall appearance compared to the other more recently collected skulls.  It stayed in South Dakota all that time which is probably not the same as if it were in a more humid environment.

So I decided to take a look at my Merycoidodon under a microscope to see if I could tell of any deterioration or other problem with the shellac coating that was applied to it back in the 1920's, almost a hundred years ago.  For reference, here's the skull.  The lighter areas are where the matrix wasn't completely removed before the shellac was applied:

 

5a99db086d92c_Merycoidodongracilis1small.jpg.2f87cce319f002d7838f669687b6e674.jpg

 

And here's what the top surface looks like under 25X magnification.  I don't see anything that would cause me concern--no cracking, no obvious dust particles.  But keep in mind this was probably stored in a fairly dry environment all those years.

 

5a99db97dd928_Merycoidodon25X.thumb.jpg.acaa09b25ed24e0a5c8db820716383fb.jpg

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21 hours ago, Sagebrush Steve said:

So I decided to take a look at my Merycoidodon under a microscope to see if I could tell of any deterioration or other problem with the shellac coating that was applied to it back in the 1920's, almost a hundred years ago.  For reference, here's the skull.  The lighter areas are where the matrix wasn't completely removed before the shellac was applied:

 

5a99db086d92c_Merycoidodongracilis1small.jpg.2f87cce319f002d7838f669687b6e674.jpg

 

And here's what the top surface looks like under 25X magnification.  I don't see anything that would cause me concern--no cracking, no obvious dust particles.  But keep in mind this was probably stored in a fairly dry environment all those years.

 

5a99db97dd928_Merycoidodon25X.thumb.jpg.acaa09b25ed24e0a5c8db820716383fb.jpg

Could well have had wax or oil mixed with the shellac. I would have expected cracking/crazing   

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2 hours ago, JohnBrewer said:

Could well have had wax or oil mixed with the shellac. I would have expected cracking/crazing   

Yes, could well be true.  I have no idea how it was prepared and from your earlier post, it sounds like adding oil was common back then.  So maybe the answer for the original poster is that if you plan to use shellac you should add an oil such as lavender oil to improve its stability.

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