Looking for trilobites

[Kane]

15 hours ago, fifbrindacier said:

 

and my first Uralichas.

 

 

(Just seeing this now... What an incredible assortment of trilobites!)

[fifbrindacier]

9 minutes ago, Kane said:

(Just seeing this now... What an incredible assortment of trilobites!)

I agree, i'm very lucky, the person with whom i made that exchange has been very generous with me. It is like @caterpillarwith the urchins, the first time we met i brought him a few urchins i gathered in a place where it is no more permitted to dig because it is classified of national interest, and he came with a big box full of urchins.

[fifbrindacier]

Here are some others found that day at Saint-Aubin-les-Châteaux.

Mostly Asaphidas and Eodalmanitidas macrophtalma, plus some Neseuretus and an Ectillaenus giganteus. They're all in clay.

 

 

 

Two tiny eodalmanitinas hide here, i had to glue the rock to get a chance to prep them.

 

This one has lost it's pygidium during the extraction but you Can see it on the imprint. I'd like to reconstitute it by doing a cast with the matrix i have. If someone could give me an advice it would help me very much. Do you think i could put some oily thing in the imprint in order the cast not to stick to the imprint ?

 

A nice nodule, but what is inside ?

 

Those Inès are from La Noë Blanche.

 

Nodules from thé fields of La Hunaudiere.

Edited June 25, 2021 by fifbrindacier

[Wrangellian]

You have done well with trilobites, for sure.

About that pygidium you want to recreate, I was thinking just a bit of clay, not too wet, just the consistency of plasticine so that it pulls off easily and doesn't leave residue on the mould (it might leave a tiny bit, but I would think clay residue wouldn't be as bad as something oily that you might not be able to remove). Put the positive side in place on the negative, then jam that bit of clay into the negative and against the broken surface on the positive at the same time - this might be be what you were planning already? - then pull it off, let it dry and then fire it in a kiln or any hot fire, so you have a durable, rock-like prosthetic that you can glue onto the positive part. I've never tried this as I don't have any pieces that need it, but I think it's worth trying. What do you think? Maybe there is a substance that is better than clay that you could use, but clay is natural and can be fired and will last as long as the rock does.

Edited June 26, 2021 by Wrangellian

[Kane]

Two-part epoxies like Milliput are the way to go for casting and filling in missing parts. They function by being malleable at first to allow carving and shaping, and cure over a period of several hours. As the substance hardens, you can use fine grit sandpapers to make minor adjustments. 

[fifbrindacier]

8 hours ago, Wrangellian said:

You have done well with trilobites, for sure.

About that pygidium you want to recreate, I was thinking just a bit of clay, not too wet, just the consistency of plasticine so that it pulls off easily and doesn't leave residue on the mould (it might leave a tiny bit, but I would think clay residue wouldn't be as bad as something oily that you might not be able to remove). Put the positive side in place on the negative, then jam that bit of clay into the negative and against the broken surface on the positive at the same time - this might be be what you were planning already? - then pull it off, let it dry and then fire it in a kiln or any hot fire, so you have a durable, rock-like prosthetic that you can glue onto the positive part. I've never tried this as I don't have any pieces that need it, but I think it's worth trying. What do you think? Maybe there is a substance that is better than clay that you could use, but clay is natural and can be fired and will last as long as the rock does.

I had the Idea to use the matrix which is the clay the Trilos are made of, reduced in power and then wet to be plastic enough, but i didn't thouht of firing it.

The pygidial spine is so fine ! I wouldn't like to have too much residue in it.

7 hours ago, Kane said:

Two-part epoxies like Milliput are the way to go for casting and filling in missing parts. They function by being malleable at first to allow carving and shaping, and cure over a period of several hours. As the substance hardens, you can use fine grit sandpapers to make minor adjustments. 

Can you put it in the imprint, let it hardening inside it and then pull off the cast ? And hiw could i give it the same color than the trilo ?

[Kane]

15 minutes ago, fifbrindacier said:

Can you put it in the imprint, let it hardening inside it and then pull off the cast ? And hiw could i give it the same color than the trilo ?

I wouldn't allow it to harden too long. What I've done in the past is put a wee bit of oil on the impression side to prevent sticking, apply the Milliput and put the nodule back together tightly, and afterward remove any of the Milliput that squishes out with a fine blade. You can smooth out any ridges between the transferred Milliput and the remainder of the positive shell to "blend" it with the other features.

 

In terms of colour matching, that takes a lot of time with trial and error using various model paints and a palette to get the right match. 

 

I'll tag @Malcolmt who has much more restoration experience than I do.

[fifbrindacier]

Thank you @Kane

@piranha?

Edited June 26, 2021 by fifbrindacier

[Coco]

On 6/25/2021 at 10:03 PM, fifbrindacier said:

Here are some others found that day at Saint-Aubin-les-Châteaux.

Mostly Asaphidas and Eodalmanitidas macrophtalma, plus some Neseuretus and an Ectillaenus giganteus. They're all in clay.

 

Very interesting ! I knew St Aubin des Châteaux but for its pyrite, not for its trilobites ! It’s a discovery !

 

Coco

[Malcolmt]

What Kane is suggesting should work. Milliput superfine white is a very good 2 part epoxy modelling compound. You could also make the part using plaster of paris in the negative. I use a silicone casting release spray but but mineral oil would work as well

[FossilDAWG]

I have a couple of questions:

1. Do you have to wash with something afterward to remove the casting spray/mineral oil?

2. How does milliput or plaster of paris replicate features that have over/underhangs or shapes that don't allow a stiff material to pull out without leaving some caught under the overhang? 

3. Is there a silicone product that is flexible enough to deal with underhangs/overhangs but also does not shrink or distort as it gels?

 

Don

[Malcolmt]

I just wipe the casting spray off with toilet paper. Milliput or plaster obviously do not work when there are overhangs. I use a product called "Mold Star 30" which is a 2 part silicone rubber for making molds. I really only use it for making a mold from a positive that I can then use to make a cast. It would not be suitable to make a missing part as it is fairly flexible when set. It is also pretty much impossible to paint to colour match. It is a blue colour. I also use raw latex for making molds. Both can be bought from Theater / Movie supply houses. This is where I buy mine from since it is a 20 minute drive from my house..... but I am sure there are ones in the USA  https://www.sculpturesupply.com/ 

[FossilDAWG]

Thanks!

Don

[Wrangellian]

I've also been having doubts about things such as oil or latex which leave an unsightly oily deposit in porous rock. I tried once to make a latex cast of a natural fossil mould and it left such an oily stain which I'm not sure how to remove without any risk of damaging the shale. In retrospect I needed something that would make the shale temporarily impermeable to oil/etc before applying the latex but I didn't know what could be used. I've never heard of casting spray. It is something you have to wipe off, and how do you wipe it off an oily surface?

Edited June 27, 2021 by Wrangellian

[fifbrindacier]

9 hours ago, Malcolmt said:

What Kane is suggesting should work. Milliput superfine white is a very good 2 part epoxy modelling compound. You could also make the part using plaster of paris in the negative. I use a silicone casting release spray but but mineral oil would work as well

Is a two part epoxy used to make a mold by putting one part in the negative and then, when the mold is hardened making a cast with the second part to have a negative i could use more than once without fearing to ruin it ?

This if i remember well the meanings of the words cast and mold of course.

Edited June 27, 2021 by fifbrindacier

[Malcolmt]

No two part epoxy means you mix the 2 parts and then a chemical reaction causes it to harden. Look up a video of using Milliput on Utube

 

[fifbrindacier]

1 hour ago, Malcolmt said:

No two part epoxy means you mix the 2 parts and then a chemical reaction causes it to harden. Look up a video of using Milliput on Utube

 

Ok, i'll do it. Thank you Malcolm