At minimum, how thick should nacre be?

[Mostawesomecoffee]

I have a pearl book that states that South Sea Cultured Pearls have nacre that represents 40 to 50 percent pearl diameter. Furthermore, it's claimed that saltwater cultured pearls, in general, have nacre of a thickness of 10 to 15 percent. Elsewhere in the book, it is stated that Japanese pearls have a layer of nacre that is "very thick" if it is at least 0.5 mm.

So, at minimum, how thick should quality nacre be for a pearl to be durable? Also, and this is a very important part of the question, does this minimum thickness vary depending upon the overall size of the pearl?

For instance, I'm sure that a pearl of 2 mm in diameter would be very durable if it were to have a nacre layer of 0.3 mm thick. If the pearl were 12 mm in diameter (with a nacre layer of 0.3 mm), would it be less durable?

thanks.

 

[R&B]

On average South Sea pearls have 2 to 3mm of nacre on the nuclei. You'll only ever know if you have them x-rayed or gently cut them in half. The pearls shape will have bearing on the overall thickness as well.
With the more formal shapes, roll them around in your fingers to see if there's any variation with the colour/tone. No variation will be an indication of a good even coating.
In relation to minimum, it shouldn't be too hard to recognise thin nacre which will mean a low grade pearl. 0.3mm on a South sea 12mm is low grade.
I could put a tray of low grade pearls in front of you and you may enjoy the sight, however upon close inspection you would notice many reasons why they are Low Grade. A tray of quality pearls would look stunning to just about anyone and close inspection would reveal the true beauty and depth of quality nacre. My point is, enjoy your books and new knowledge from the post's on this guide, but, get out to some trade shows or farms and feel some pearls. Sight and touch is the secret to learning about South Sea Pearls. I've probably not totally answered you but good luck with your discovery of knowledge about Pearls.

 

[Mostawesomecoffee]

All this time later, I realized that I need some clarification.

When it's said that the nacre is 2 mm to 3 mm in thickness, I'm not sure what is meant by this. If a straight line were drawn through a pearl, is it being said that:

Situation 1: The line would pass through 2-3mm of nacre, then through the nucleus, then through 2-3mm of nacre giving a total of 4-6mm of nacre?

OR

Situation 2: The line would pass through 1-1.5 mm of nacre, then through the nucleus, then through 1.1.5 mm of nacre giving a total of 2-3mm of nacre?

 

[pattye]

Situation 2, I believe.

 

[Pearl Dreams]

What Pattye said. In other words, the nacre would be 1.0-1.5mm thick, measuring outward from the surface of the nucleus in all directions (assuming the pearl was perfectly round.)

The nacre in your example accounts for 2.0-3.0mm of the diameter, but only 1.0-1.5mm of the radius.