Making latex casts and molds of trilobites

[aek]

A few days ago I found a nice  internal & external mold of a rare Arctinurus sp. This is something I've been looking for over 5 years. I was beginning to give up hope having never even found a pygidium in these rocks. Anyway, I decided it would be good to make some internal/external latex casts and molds and show progress here since I haven't seen much on this topic. I am doing this to observe any differences in the internal/external shells since with this type of preservation the skeletal shells have been dissolved during dolomitic diagenesis. The outer shells could possibly exhibit different features not observable in the internal molds ie. taphonomic or morphological, etc.

 

From making comparisons,  I don't think it is A. occidentalis as the anterior border projection is not as pronounced. A. nereus more pustulose and lacks anterior tongue. It more closely resembles A. boltoni but I don't think is reported from this area. So, I guess it is unknown...for now unless  @piranha can identify it. 

 

 

 

First cleaned up with scribe and carefully removed the "tongue" from matrix and superglued in place.

 

 

 

 

This appears to be very easy but actually took many hours. Also not shown is the more complicated prep of the external mold which had to be broken into three pieces and trimmed with a tile saw and then glued together. Set overnight. 

Aside from the Arctinurus, I  also am making latex casts/molds of Dalmanites platycaudatus and a Glyptambon verrucosus cephalon. I don't have a lot of external trilobite molds as they usually break apart and lost in the field. This is also my first attempt at making internal latex molds from externals using hydrocal. I have made latex casts from internals with plaster of Paris but with mixed results as it is softer and more easily broken. For these I want high fidelity examples. Also, I am just winging it.

 

Here, applying a very thin first layer of latex to the external Arctinurus mold. The first 4 or 5 layers need to be very thin and dry between applications.

 

I decided to attach the cephalon /pygidium to the dalmanites with clay and aluminum foil to hold both parts together.

 to be continued...

Edited January 24, 2022 by aek

[aek]

Next applying clay around edge of the internal . 

 

 

Edited January 23, 2022 by aek

[piranha]

'Arctinurus' nereus is classified now as Dicranopeltis nereus.

 

Arctinurus boltoni is reported from the Racine Dolomite in Kankakee which also includes Glyptambon within the same community faunal association.

[aek]

16 hours ago, piranha said:

'Arctinurus' nereus is classified now as Dicranopeltis nereus.

 

Arctinurus boltoni is reported from the Racine Dolomite in Kankakee which also includes Glyptambon within the same community faunal association.

Interesting, I wasn't aware Arctinurus boltoni could be found in the Racine. However, this was actually found in the Sugar Run along with Ommokris and Sphaerexochus remains in the same block. Is boltoni also found in the Sugar run? 

[aek]

Ok, here is more progress. layers of latex .

 

After applying about 13  successively thicker layers , and using a blow dryer to help speed up the process. This will probably take all day to dry...as it drys will add more latex until the cavities are completely filled.

[piranha]

2 hours ago, aek said:

Interesting, I wasn't aware Arctinurus boltoni could be found in the Racine. However, this was actually found in the Sugar Run along with Ommokris and Sphaerexochus remains in the same block. Is boltoni also found in the Sugar run? 

 

Arctinurus sp. is listed from Sugar Run. I sent the photo to a lichid specialist friend. Stay tuned for additional info....

 

[Sjfriend]

Nice topic. I've wondered about doing something like this but that's as far as I ever got 

[Bobby Rico]

This is indeed interesting thread looking forward to seeing how much detail you get when casted,

 

cheers Bobby 

[piranha]

Here is the reply from the lichid specialist:

 

Quote

"It certainly looks like A. boltoni in terms of the shape of the anterior border. A. thompsoni Miller & Unklesbay, 1944 was said to be from the Joliet Dolomite but I don’t know whether that is true as the Joliet is now defined. That species is known only from pygidia, unless the fragmentary cranidium illustrated by Weller (1907, pl, 20, fig. 12) belongs to it."

 

 

Included below is figure 12 referenced from Weller 1907 (listed incorrectly by Weller as A. occidentalis) that could possibly belong to A. thompsoni....pending any significant future discovery that could determine more conclusively by an association of cranidia and pygidia within the same strata. In the meantime, you can label it Arctinurus cf. boltoni or more conservatively as Arctinurus sp.

 

 

Miller, A.K., Unklesbay, A.G. 1944

Trilobite Genera Goldius and Arctinurus in the Silurian of Iowa and Illinois.

Journal of Paleontology, 18(4):363-365

 

Weller, S. 1907

The Paleontology of the Niagaran Limestone in the Chicago Area: The Trilobita.

Natural History Survey, Chicago Academy of Sciences, 4(2):163-281 PDF LINK

[aek]

20 hours ago, piranha said:

Here is the reply from the lichid specialist:

 

 

 

Included below is figure 12 referenced from Weller 1907 (listed incorrectly by Weller as A. occidentalis) that could possibly belong to A. thompsoni....pending any significant future discovery that could determine more conclusively by an association of cranidia and pygidia within the same strata. In the meantime, you can label it Arctinurus cf. boltoni or more conservatively as Arctinurus sp.

 

 

Miller, A.K., Unklesbay, A.G. 1944

Trilobite Genera Goldius and Arctinurus in the Silurian of Iowa and Illinois.

Journal of Paleontology, 18(4):363-365

 

Weller, S. 1907

The Paleontology of the Niagaran Limestone in the Chicago Area: The Trilobita.

Natural History Survey, Chicago Academy of Sciences, 4(2):163-281 PDF LINK

Thank you for this information, greatly appreciated.  The Joliet formation lies below the Sugar Run starting with Savage 1926.  Willman 1973 divided the Joliet into three members and this continues to present. It's difficult to determine which member  of the Joliet they are referring to but according to, Miller, A.K., Unklesbay, A.G. 1944 the pygidia was found in the now flooded Bonfield quarry. 

[aek]

So here's more progress. To mix hydrocal, first add water to a cup then slowly add hydrocal until you can add no more.

 

 

 

Stir as little as possible to not create more bubbles but enough to ensure no powder remains. Then coated the white specimen tray with Vaseline and added hydrocal to it and placed the internal Artinurus mold upside down into it to dry.

 

 

Since I made way too much hydrocal, I used the excess to make additional casts of other  trilobites. No idea how long hydrocal takes to dry but I'll probably just let these sit overnight.

 

[aek]

The latex casts of the external molds are finally finished after 4 days of layering. I'm having some trouble casting hydrocal free of bubbles. I'll have to experiment adjusting the viscosity or something. Anyway, the latex cast reveals that the external exoskeleton of the Arctinurus is smooth, unlike the interior which exhibits tubercles as shown in the pics below. It's also interesting that the latex even records the fine dolomite crystals creating a sparkly cast. 

 

 

Latex cast from external mold showing dolomite crystals, smooth exterior sculpture. The line extending from anterior through the right glabellar lobe is from having to break the external mold to make the cast.

 

Original fossil internal mold showing tubercles texture.

 

Internal mold cast showing bubbles.

 

 

D.platycaudatus smooth exterior cephalon.

 

 

Glyptambon tuberculose exterior.

 

 

Thanks for reading.

Edited January 26, 2022 by aek

[AK hiker]

Having much experience in my dental office with impressions and pouring models can comment on this. The problem of bubbles/voids in the poured material can be corrected by mixing your material in a vacuum mixer. Pour slowly while vibrating the impression to not trap air in the depressions.
 

Seeing the multiple voids on the internal mold cast makes me think the mold was possibly degassing and creating the bubbles