What D50 Actually Tells You About Diamond Powder (And What It Hides)

Diamond micron powder is sold by grade: 0–2, 2–4, 4–8, and so on. Two producers quote the same grade. One costs 30% more. Both certificates say D50 = 1.4 µm.

They are not the same material, and the certificate is not lying.

What D50 means

D50 is the median of the particle size distribution by volume: half the particles are larger, half smaller. It is a single number summarising a curve, and like any single number summarising a curve, it discards most of the information.

Two powders with identical D50 can have:

Different distribution widths (one tight, one broad)
Different tails above the upper limit
Different shape distributions
Different agglomeration behaviour

For lapping and polishing, the tail above the upper limit is what matters most. A powder nominally 0–2 µm with a 12% fraction above 4 µm will scratch a surface you expected to polish, because a 4 µm particle removes material like a 4 µm particle regardless of what the grade label says.

Reading a distribution curve

Ask for the full distribution data, not the certificate summary. What you want to see:

Metric	What it tells you
D50	Median — the headline number
D10 / D90	Spread — how wide the distribution is
D99	The tail — the largest particles present in meaningful quantity
Span ((D90−D10)/D50)	Normalised width — comparable across grades

A tight grade for precision polishing might have a span under 1.0. A broad grade with the same D50 might exceed 2.0. Same certificate headline, completely different behaviour.

The measurement method matters too

Laser diffraction, sedimentation and sieve analysis give different distributions for the same powder. They are not interchangeable.

Laser diffraction — standard for micron grades, fast, but sensitive to dispersion protocol
Sedimentation — slower, better for sub-micron, sensitive to agglomeration
Sieve — only meaningful above roughly 20 µm

If two producers report D50 values measured by different methods, the numbers are not directly comparable. Ask which method, and ask for the raw data.

What we insist on

For any micron powder order, we require:

Laser diffraction report with the full curve, not a summary line
D99 stated explicitly, so the tail is visible
Sample retention — a sealed reference sample from each lot, held twelve months
Independent verification on first order from a new producer

The fourth point is the one that changes outcomes. A producer’s own report describes what they intended to ship. An independent measurement describes what they shipped.

The price difference, explained

When one producer is 30% cheaper on the same nominal grade, the difference is usually one of:

Broader distribution (more tail, less precise grading)
Different measurement basis (sieve-derived figures for a micron grade)
Different source material (recycled or lower-grade feedstock)

None of these are necessarily disqualifying — a broad grade is fine for some applications. But you should be buying it knowingly, at a broad-grade price, not paying a precision-grade price for it.

Sourcing micron powder? Send the grade and application — we will come back with full distribution data, not just a D50.