A well-known phrase associated with Jingdezhen compresses an ideal of porcelain into four images:

White as jade. Bright as a mirror. Thin as paper. Resonant as a chime.

It sounds like poetry, and it is. It is also a useful vocabulary for looking: colour, surface, thinness and sound. None is a universal pass/fail rule for every porcelain tradition, but together they invite closer attention to what a piece is doing.

1. White as jade — the material test

Not white as snow, note, and not white as paper. Jade.

The distinction is exact. Snow-white is a dead, blank white — the white of optical brighteners and modern sanitaryware. The white of fine porcelain is alive: faintly warm or faintly blue-green depending on the clay and glaze, with depth under the surface, like light entering a stone rather than bouncing off a wall.

What it measures: the purity of the kaolin and porcelain stone, and the honesty of the firing. Iron contamination in the clay fires gray or yellow-brown; underfiring leaves the body chalky and flat. That soft, deep, jade-like white can't be painted on — it is the material, refined and fully transformed. When you see gray-toned porcelain sold with bright white glaze poured over it, someone is compensating.

Run the test: look at an unglazed area — the foot ring underneath. Fine porcelain shows clean white there, not gray or beige. Then look into a glazed surface at an angle: quality reads as depth, not as brightness.

2. Bright as a mirror — the glaze test

A great glaze is a sheet of glass a fraction of a millimeter thick, melted evenly over a curved object at 1,300°C. Getting it to come out flawless is quietly heroic: too thin and it starves, showing dry patches; too thick and it runs, pools, and drips onto the kiln shelf; fired unevenly and it blisters into pinholes or clouds into dullness.

"Bright as a mirror" is the pass condition: a surface so evenly fused that it reflects like still water. What it measures is control — of glaze chemistry, application, and above all the kiln.

Run the test: hold the piece so a window or lamp reflects in the glaze, then tilt it slowly. The reflection should stay coherent and glide across the surface. Orange-peel texture, pinholes, or hazy patches mean the fire won that round. (One nuance: some glazes — matte and crystalline finishes — aim elsewhere deliberately. The test applies to glazes that intend to be glassy, which classical Jingdezhen glazes do.)

3. Thin as paper — the confidence test

Here's the counterintuitive one. Thinness in porcelain is not fragility — it's a display of strength.

Only fully vitrified, high-fired porcelain has the structural integrity to be worked thin and survive. Earthenware made paper-thin would crumble; stoneware would crack in the kiln. So when a Jingdezhen potter throws a bowl whose walls taper to a couple of millimeters at the rim, the thinness is a signature: this material is so strong, and my control so exact, that I can afford this. At the extreme end, the city's famous eggshell porcelain has walls under a millimeter — you can read text through them.

What it measures: both the material (fully fused, glass-like body) and the maker (a trimming hand steady enough to shave a spinning, leather-hard form down to near-translucency without holing it).

Run the test: hold the piece up to a bright light. High-fired porcelain transmits a warm glow — you'll see your fingers' shadows through the wall. And weigh it in your hand: fine porcelain always feels lighter than your eye predicted. That small surprise is the test result.

4. Resonant as a chime — the integrity test

The last test is the most unforgiving, because it checks what you can't see.

Flick the rim of a fully vitrified, structurally sound piece and it rings — a clear, bell-like note with real sustain. The physics is simple: a dense, glassy, uninterrupted body carries vibration beautifully. Anything that interrupts the body kills the note. Underfired ware answers with a dull knock. And a piece with an invisible hairline crack — the flaw that no visual inspection catches — doesn't ring at all; it buzzes, dead on arrival.

The ring test can offer a clue about integrity, but shape, thickness, handles, applied decoration and the way a piece is held all change the sound. It is not a guarantee of complete vitrification or the absence of every hidden flaw.

Run the test: rest the bowl or plate lightly on spread fingertips (gripping it damps the note), and tap the rim gently with a fingernail. Listen for pitch and sustain. If a familiar piece suddenly sounds dull or buzzes, inspect it carefully before further use.

Four tests, one philosophy

Notice what the four tests have in common: none requires trusting the seller. No certificate, no brand story, no label — just your eyes, your hands, and your ears against the object itself. A thousand years ago that was how you bought porcelain from a stranger's kiln lot, and it embodies an idea worth keeping: quality should be verifiable by the person holding the piece.

Use the four phrases as prompts, not promises. Hold a piece to the light, notice the foot and glaze, feel its balance and listen gently. Then compare those observations with the material and care notes supplied for that individual piece.

The old standard still works. So does the porcelain.