Hydrostatic weighing, my method

Why weigh rather than look

The word jade covers two unrelated minerals. In 1863, Alexis Damour established that what was called jade is sometimes a jadeite, a pyroxene, and sometimes a nephrite, an amphibole of the tremolite actinolite series. Two families, two hardnesses, two prices.

And alongside them circulate two imitations so widespread that they have become the norm on some shelves: serpentine, sold as “new jade”, “Korean jade” or “olive jade”, and dyed quartzite, sold as “Malaysia jade”. None of these labels means jade.

To the eye the confusion is easy, and it is made every day, including in good faith. A well polished serpentine has the green, the cool touch and the translucency you expect. What does not mislead is density: it separates these four materials without ambiguity, and it can be measured on a kitchen table.

The protocol, in order

It is a kitchen gesture rather than a laboratory one, and that is exactly why it is worth something: anyone can repeat it with what they have at home, and check what I write.

1. I weigh the stone in air, dry, without a setting, on a scale accurate to a hundredth of a gram. I call this mass m_air.
2. I hang it from a very fine thread, long enough for the stone to hang freely, and I lower it completely into a glass of water standing on the scale, without letting it touch the bottom or the sides.
3. I read the second mass, that of the submerged stone, m_water. It is always lower: the water pushes the stone up, by exactly the weight of the volume it displaces.
4. I divide: the density is m_air divided by the difference between the two masses. The result has no useful unit here, it is a ratio to water.
5. I start over three times and keep the average. A single air bubble clinging under the stone is enough to spoil a reading, and it is not always visible.

I note the date, and I publish the three numbers on the product page: the mass in air, the submerged mass, and the density obtained. Exactly what each product page carries.

The four reference points I compare against

These values come from the mineralogical literature. None of them is a measurement taken on a piece from this shop: they are the bounds, and my own measurements live on the product pages.

The gap that matters reads at a glance: between a nephrite at 2.95 and a serpentine at 2.6 there is a third of a point, far beyond the uncertainty of a kitchen scale. Between a jadeite at 3.3 and everything else, there is not even a discussion.

One example per listing, and not every piece

This is the point I insist on writing in full, because the opposite wording would sell better and be false.

So you receive a piece of the same listing, not the one I held. On a natural material, that means the green will not match the photo to the millimetre, and I would rather say it before than after. In exchange, you know what the listing contains, which is already rare in this market.

And when a stone reaches me already set or already strung, I publish no figure at all. Writing the gap rather than a plausible value is the rule of this shop.

The three things this measurement does not prove

A method presented without its limits is not a method, it is a sales argument. Here are my three, and they are serious.

1. It says nothing about treatment

A jadeite bleached with acid and then impregnated with resin is still a jadeite, and the resin does not change the mass enough to show. The A, B and C classification, which describes exactly these treatments, cannot be read on a scale: only infrared spectroscopy in a laboratory settles it, and I do not have one.

My supplier does not know the status of their stock. That is not an incident, it is the ordinary state of this market. So I never write “grade A jadeite”, “type A” or “untreated” on my product pages: the treatment status is not determined, and the information sheet explains it in detail.

2. Metal and thread throw it off

A set stone weighs with its setting, a bead strand weighs with its thread, and silver is far denser than jade. The measurement is therefore only worth taking on the bare stone of the example. When I cannot take it apart, I do not measure, and the product page says so.

3. It loses its meaning on very small pieces

On a four millimetre bead, the uncertainty of the scale becomes the same order as the gap between 2.95 and 2.65. The figure still exists, but it no longer decides anything. On those pieces I rely on what I see and on where the batch comes from, and I say so plainly.

I weigh, I do not certify

I have no gemmology degree and I do not claim one. This page describes a reproducible physical measurement, not an expert appraisal, and the figure I publish is not a certificate: it is a reading, with its date, that you can redo.

On a disputed case, my answer is that I cannot settle it. That is less comfortable than a laboratory logo on a product page, and it is the only thing I can stand behind.

• The treatment information sheet
• Where my jade comes from
• Spotting real jade
• See the shop