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Differences in fossil preparation


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Hello,

 

As I'm sure most have seen, certain fossils sometimes have a white or cream colored "halo" around them and other times the same type of fossil doesn't. I'm wondering.... can someone explain why this is? I personally always prefer specimens without the halo purely from an aesthetic perspective. But I'd be curious to learn more about why this is done and also whether or not other people prefer one way over the other. Is one way considered more desired than the other way, should one expect to pay a significant premium for one over the other? etc. Thanks very much! And to show you what I'm talking about... here are some examples of specimens I've seen from the same location where one has a halo and one does not. It's obvious, but in each of the three examples the first example does not have a very noticeable halo and the second example does have it.

 

image.png.fc9ed7cf313676a1bca64a8cfceb449a.png

 

image.thumb.png.3d128d22baa3ba599c89e65954b42e3c.png

 

 

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Is this not just a case of the fossil prep work and how aggressive the preparator was in cleaning the edges next to the fossil?

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10 minutes ago, grandpa said:

Is this not just a case of the fossil prep work and how aggressive the preparator was in cleaning the edges next to the fossil?

 

@grandpa - certainly could be - I'd believe it! So, in that case, is this just a matter of the skill of the preparator? I.e. on any of these specimens that have what I'm describing as a "halo", this effect could have been avoided if the preparator had more skill or used more care? And accordingly less of the "halo" is more desireable to most people?

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It may also be out of preference (by the preparator or client). Some fossils may seem to "pop" more in being given this halo to contrast it with the surrounding matrix. This would certainly be the case where a specimen is the same tone/colour as the matrix.

 

In most of the examples posted above, I would wager it was haste or inexperience. That being said, preparation is also a kind of art, and it may come down to preference. For example, some people prefer the fossil to appear on a natural-looking matrix, while others like the landscaping to be smooth. 

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@fossilguy312 The 1st image of the trilobite and the 1st of the starfish provide an excellent illustration of the phenomenon of your observation. The "halo" is a very natural and expected outcome of disturbing the natural matrix. Look closely at the two images I cited. Contrast the surface texture of the undisturbed matrix (split-out or weathered). You will see that it displays marked texture vs the area within the "halo" which has been mechanically "smoothed." This is the simple, natural byproduct of the needed removal via abrasion of the obscuring matrix. The notably different surface textures, even though they are the same material in both areas, cause light to be reflected in very different ways. Air abrasion will leave a different  "halo" texture than scribe work; but the results of both will differ from the appearance of the native, undisturbed matrix. Some folks follow scribe work with air abrasion to smooth the worked area. Reaction to the "halo" appearance really is a matter of aesthetics with appeal varying from person to person. The different appearance, however, between a mechanically disturbed area and pristine matrix is unavoidable, if prepping is to proceed.

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Uncle Siphuncle

Sometimes the halo can be calmed by light scrubbing action with a wet toothbrush, other matrices may require a microblast with appropriate media, at other times a light, controlled, localized acid etch may restore surface character of the matrix close to what it was before.  Some folks may even follow up with color matched, watered down acrylic paint to restore color.  I don’t like the disturbed look, personally.  My goal is an appearance of being prepped by nature, not a signature of the preparator.

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@snolly50 - thanks for your reply - completely see what you're saying and agree with you on all counts. Let me be a bit more specific then in my question. Take the two starfish pieces as an example. They are both similar species from the same rock formation (Bundenbach... i.e. Hunsruck slate). So they have the exact same matrix. Agree with you that they both have the halo and that this is pretty much impossible to avoid if the fossil is going to be prepared, but why is the first halo black and smooth (and in my opinion, fairly unobtrusive and dare I even say beautifully done :-) ), vs. the second halo which seems like a hazy/cloudy white that is in my opinion much less attractive than the first? Is this because one used a certain matrix removal method and the other used a different one?

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I usually use a light pass with acid after prep to get rid of that halo. Got to be extra careful with that with some delicate fossils like this trilobite though .

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