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Coating / Sealing shale fossils for presentation


Rocky Stoner

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Hello friends,

   As you may have noticed, I have recently found quite a few nice fossils in soft shale.

I clean the shale with a scrub brush and water and they look really good while still wet.

When they dry however, they loose much of their luster as the features become quite hard to pick out, especially when trying to pick them up with the camera. Just prior to taking a pic for a post, I wet it with water using a soft paintbrush then blow any surplus water off with compressed air and get the pic right away. This works fairly well for the pic, but it soon dries out again.

I experimented with a light brushing of mineral oil which looks very good, but it eventually dries out as well. Only did one light coat.

I'm reluctant to try shellac, polyurethane or any clear-coat or sealer for fear of doing irreparable damage to the appearance of the more delicate features.

I'd like a very thin gloss / semi-gloss finish that enriches the appearance for a better 3D presentation.

Any tips, tricks or links ?

 

Thanks again.

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I don't generally coat my fossils so I can't really help you, but whatever you use, I would recommend against anything that is glossy, as any sort of glare will interfere with getting good photos. If you can find something that give it a wet but not glossy look, use that (and let us know what it is). I once used PaleoBond (cyanoacrylate, like Crazy Glue) on a Ice Age mollusc in loosely-consolidated sand, and it worked well (though it very much darkened the sand), but when I tried it on an ammonite it just made a sticky mess. Everything seems to be hit and miss! which makes me leery of trying anything else..

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For general preservation I usually use "paraloid" which is a mix of small plastic beads and acetone. Also a mixture of wood or craft glue with water. Depending on the ratio, you can get achieve a fairly glossy finish. If you want more info feel free to ask.

And as Wrangellian said, high gloss isn't a great idea (I learned the hard way D: )

Also, this could be useful (I think?):

 

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Dilute Dextrine is a good water soluble coating. Very little film build up, it increases contrast, neutral color change, luster doesn't get much past matte finish and can be removed with water.

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Thanks folks, I'll research your suggestions.

I agree full gloss is no good. That is why I hit it with the air gun to bring it down to a semi gloss, bordering on flat but retaining the contrast and definition from the wetted surface. Somewhere in the middle would be perfect but must be thin enough to not clog the delicate byrozoans.

I have a hundred pounds or so of samples to experiment with.

Maybe I'll start a topic to document and share my findings and progress (if any).

Thanks again Gents,

kindest regards.

 

 

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4 hours ago, fossilcrazy said:

Dilute Dextrine is a good water soluble coating. Very little film build up, it increases contrast, neutral color change, luster doesn't get much past matte finish and can be removed with water.

Where do you get that stuff?

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Hi,

 

I revived the colors of some of my fossil sea urchins with some colorless shoe polish. Colors return as if they were wet. When we want to remove this effect it is enough to cross them under the water with a small brush and a little soap.

 

Coco

 

----------------------
OUTIL POUR MESURER VOS FOSSILES : ici

Ma bibliothèque PDF 1 (Poissons et sélaciens récents & fossiles) : ici
Ma bibliothèque PDF 2 (Animaux vivants - sans poissons ni sélaciens) : ici
Mâchoires sélaciennes récentes : ici
Hétérodontiques et sélaciens : ici
Oeufs sélaciens récents : ici
Otolithes de poissons récents ! ici

Un Greg...

Badges-IPFOTH.jpg.f4a8635cda47a3cc506743a8aabce700.jpg Badges-MOTM.jpg.461001e1a9db5dc29ca1c07a041a1a86.jpg

 

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I ran into a similar problem with some plant imprints I had found. The imprints on the shale slabs were very delicate and it was a bit hard to see all of the detailed features without the proper lighting. I wanted to find a way to highlight the fossils while preserving the imprints so they wouldn't get rubbed away over the years. It was suggested that I coat the fossils in a PVA Acetone solution. Take a look at the thread below that discusses this process. This is now a standard procedure for any delicate plant imprints I find.

 

Coating fossils in a dextrine solution is a good way to highlight the fossils, but it won't provide help to preserve the fossils.

 

 

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Get YELLOW dextrin from a taxidermy supply house.  Mix the powder into warm water.  I don't deal with many inverts, and I never found the need for nor developed the technique for using my supply.  It is a superficial coating with NO preservation value.

 

Here is a workable technique for consolidating fossils. [Also posted in MY PROFILE / ABOUT ME]

Polyurethane will not give the desired penetration of the fossil. This resin is very difficult to remove. Putting polyurethane on a fossil is usually a bad idea.

I recommend against white glue (polyvinyl acetate) as a consolidant because there are better materials available.* (Normal prep lab dilution of white glue is one part water to two parts glue.) Rarely, a specimen cannot be dried without it crumbling, and white glue is the only reasonable answer. In my experience, white glue is messy and never looks good when the specimen is fully-prepared.

A much better material for bone is a polyvinyl butyral plastic such as Butvar B-76, but that material may be hard to find in small quantities. I have used this plastic, dissolved in acetone, for many types of fossils. (I have used it successfully on Silurian-age shales with brachiopods, for example.) It penetrates well, and in the proper dilution it produces a "damp-looking" finish with no gloss.

Butvar B-76 (but not other Butvar varieties) is also soluble in alcohol. (I assume that is denatured alcohol that you can buy in gallon cans.) I have never tried this solution for consolidation. The alcohol takes considerably longer to boil off the treated specime

Butvar B-76 and other suitable plastics, such as Vinac, are more frequently available on the Internet these days. But, if you can't find Butvar-76 or Vinac, you may want to fall back on a solution of Duco Cement (clear, like model airplane glue) in acetone. Duco Cement is not a first choice, or even a second; but, it will hold a fossil together while you consider other options.

Dilution? Start with a tube of glue dissolved in about five or six ounces of acetone in a glass jar with a metal screw-top. Shake well.

(From this point, the techniques are the same for any plastic consolidant you choose.) Adjust the dilution with more acetone until, after shaking, the tiniest air bubbles are just slightly retarded in their rise to the surface.

I usually heat specimens with an infra-red lamp to drive off moisture just before dipping the fossil. I do this with all sorts of fossils, and have never had one damaged by the heating. The untreated specimen is always at least as wet at the relative humidity of the air around it, I surmise. (A microwave oven may be as effective, but I've only dried glass beads for my air-abrasive unit.) Residual moisture may cause a white film to develop on the surface of a fossil after dipping in the consolidant.

 

Here's how the white film forms: As the acetone in the consolidant evaporates, the temperature at the surface of the specimen chills abruptly, lowering the dew-point at which ambient water vapor condenses.

 

And, that's my theory -- that the white film has two potential sources: residual interstitial moisture and ambient humidity condensing at the surface chilled by evaporation.

 

Think about a plastic bag of food placed into a freezer, where frost is moisture and bag is the film of consolidant. Frost can form on either or both sizes of the plastic bag, inside frost from moisture in the food and outside frost from atmospheric moisture.

 

My solution is heating the specimen to drive off residual moisture, and consolidating while it is warm to increase the dew-point at the specimen's surface, inhibiting condensation as the acetone boils off.

Do NOT heat the acetone solution directly. The acetone solution will get warm after dipping a number of heated fossils. You must have good ventilation to deal with the fumes!

I use a long-jawed forceps -- ten-inch tweezers, really -- to dip and/or retreive the fossils from the jar.

Ideally, you would submerge the dry specimen in this consolidant for a brief time (say 10-30 seconds, or until the specimen stops fizzing). Set each wet specimen aside to dry on cardboard (I use a beer-flat because that cardboard is absorbant and doesn't readily stick to the fossil).

To avoid pooling of consolidant which may drain from a bone, I rotate the bone once or twice in the first minute or two after placing it on the cardboard. This helps avoid a "drip-bead" of consolidant near the lowest point of the bone.

For a specimen too thick to be submerged, you can use a turkey-baster to flood the difficult areas. I treated an adult mammoth tibia that, because of its size, I dried in the Florida sun, then used the baster to pump consolidant into every opening of the bone.

I use a RubberMaid-type container to hold the consolidant for this basting step - that plastic seems to be impervious to the acetone. Get 'em at your local dollar-store.

Acetone evaporates very quickly. Replenish the consolidant mixture with a bit of acetone if you are using it on many specimens. Store it in a tightly sealed glass jar. Even if some acetone evaporates away between uses (it always does, it seems), you can reconstitute the solution by replacing the acetone.

Acetone is a nasty solvent. The fumes are explosive. The fumes are toxic. The liquid penetrates the skin-blood barrier. It's best to use gloves. Use in a well-ventilated area.
--------------Harry Pristis

http://pristis.wix.com/the-demijohn-page

 

What seest thou else

In the dark backward and abysm of time?

---Shakespeare, The Tempest

 

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