Is the nacre in the pictures of these shells "flawed"?

[Mostawesomecoffee]

Hi,

I have two shells of the same species of freshwater mussel. Both shells were rather old when found, with the interiors entirely covered with a chalk-like layer. I'm guessing that they were lying around the lake shore where I found them for at least a year, if not longer. I cleaned both shells with sandpaper, then with 0000 stel wool. The first picture is of the nacre of the larger shell after being cleaned in this manner. The subsequent pictures are of the smaller shell which, in addition to being subjected to the aforementioned treatments, was placed in hydrogen peroxide for a few hours. This did very little. The shell was then rinsed off, and placed in bleach (about 1:1 bleach to water ratio) for about twelve hours.

My question concerns the gold coloring seen in the nacre. I'm wondering if this is a harmless variation or a flaw. The gold coloring can be seen very clearly in the first picture (the large shell). This gold coloring looked the same in the smaller shell prior to bleaching. During bleaching, pieces of the periostracum loosened up, as well as this gold area. The overall size of the gold area shrunk. As can be seen in the picture (of the smaller shell) the gold area is rimmed with white. This white color is where the bleach has undercut the gold area. This white undercutting can be seen to a minor degree in other parts of the small shell, but not as dramatically as in the gold area. In the second photo, the gold area is/was in the deepest part of the shell.

The third picture is also of the smaller shell, but lit from the back. The gold area seems to be more opaque than the rest of the shell.

So, it seems that either the gold-colored area is a "flaw" with regard to the rest of the nacre (i.e., composed of something heavy in protein that's not as durable as the rest of the nacre) or the entire shell has been damaged by extreme bleaching, and the gold area is in no way weeker than any other part of the shell.

What are your thoughts?

Thanks.


View attachment IMG 1841

 

[CeciliaW]

I'm confused. You used sandpaper and steel wool on nacre and wonder if it's flawed? What was the purpose of such harsh treatment?

 

[Mostawesomecoffee]

I'm confused. You used sandpaper and steel wool on nacre and wonder if it's flawed? What was the purpose of such harsh treatment?

The shells were very old when found. They looked nothing like the shells in the pictures. The nacre (as it is) wasn't visable at all. The interiors of the shells looked like they were entirely covered in chalk. At that point, I didn't know if the shell was even good underneath.

 

[Caitlin]

Maybe Dave will see this post.

Meanwhile however, I think that gold layer is made out of the proteins that are part of the construction of the shell. It is called "conchilion" (sp) It binds the tiny platlets of calcium carbonate in layers and the layers intertwined together cause the pearly look to the shell. It seems like your cleanup exposed a protenaceous layer. Old calcium carbonate that has lost its protein, looks powdery and soft as you described the shells to be before cleanup.

 

[Lagoon Island Pearls]

I'm not sure what the OP means by "flaw". The term is used when grading finished pearls, but not necessarily anomalies in physiology.

After all, despite the sample being partially degraded naturally then subsequently destroyed by mechanical and chemical means, it appears to have normal growth fronts.

 

[SunSeeker]

What would be the proper treatment for (non-destructive) cleaning of shells?

 

[Lagoon Island Pearls]

However it's intended use would determine treatment. For scientific or analytical purposes, the best treatment is none, apart from washing in cold water then wiped clean. Soft scrubbing with a salt slurry is a recognized practice for cleaning pearls. Once cleaned and allowed to dry for few days, a light coating of mineral oil will prevent cracking and fading.

Harsh chemicals destroy otherwise measureable components or leave traces that can skew results or cause other changes over time.

In nature, shells from mollusks breakdown after death. The first thing that disappears is the protein component, after all it's mostly water soluble . Next, the aragonite tablets revert to calcite then slowly dissolve into the water column or sediments. In some locations, shells become a component of beach sand.

The best time to collect shells is perimortem (at or near death). If shells are intended for display, the periostracum can be removed by sanding or sand blasting, but the nacreous surface should be protected during the process.