[Caitlin]

Somewhere on this site, I think it was mentioned that everyone "polishes" pearls. What is the best way to do this? Do people artificially enhance luster? If so, how, and is it possible to tell?

Caitlin

[jshepherd]

Hi Caitlin,
Pearls are usually always polished. This does enhance the shine and luster of the pearls. This is a very common practice, as is bleaching and pinking.

Another method of enhancing the luster of pearls is through heat treatment. This is done quite often to very low-luster pearls. These are the pearls with the thin nacre but high luster.

I actually have several pictures of these processes at a factory in China. I will see if I can size them and put them in this thread.

[jshepherd]

This is a photograph I took of a classic Chinese polishing machine. Please keep in mind that only small factories use such a rudimentary machine.

[jshepherd]

This is from the same factory. This machine is used to clean the pearls fresh after harvest.

[jshepherd]

This is a small bleaching room - again at the same factory.

[jshepherd]

Finally, this is the machine used to treat the pearls with heat. Although this increases the luster of the pearls, this may damage the nacre. Heat treatment is not a recommended treatment. The luster will eventually fade.

[Caitlin]

Wow! Great pictures! Our jshepherd is as much anthropologist as pearl master!

If you haven't read his bio @ PP.com, here's a link http://www.pearlparadise.com/aboutourfounder.html

I am guessing that the pictures are of Akoya pearls.

Are FW pearls treated with heat (or anything else) to increase luster?

What kind of bleach is used on pearls?

[jshepherd]

Hi Caitlin,

Just noticed I had not responded to your question from January! I am sorry about that!
The pictures from that factory were all Akoya pearls.
Freshwater pearls are treated with bleach after they have been drilled (typically). This is the reason one rarely sees a lot of undrilled loose pearls. The bleaching can make them a little more brittle to the drill. Bleaching with freshwater pearls is nearly 100% universal. Freshwater pearls are also polished to enhance luster.

The bleach used in the pictures is a very mild type of bleach. The main active ingredient is H2O2, aka Hydrogen Peroxide. There are a lot of other chemicals used such as Na2CO3 (Sodium carbonate). One chemical actually reacts with the lights, which is why the bleaching rooms are filled with lights. The rooms are also temperature controlled, always below 20 C.

The bleaching solution is not universal. Every factory actually mixes chemicals on site. The success or failure of a factory depends heavily on the skills of the chemist mixing the ingredients. If the bleach is too strong the pearls can be damaged (appear very chalky), if the bleach is too weak the desired effect will not be achieved.

[Kevin Canning]

I think it is also important to note that the amount of time the pearls are bleached depends on the quality of the pearls when harvested. Each of the jars are filled with a specific quality of pearl. The highest may only be left in the bleach for a couple of weeks, while the lower quality (poor color) pearls may be left for up to 6 months.
In the picture below I am examining one of the highest quality jars of Akoya pearls. This is an Akoya pearl factory which I visited on my last trip out to the pearl farms.

Kevin Canning
President
www.PearlsOfJoy.com