Ash is what remains after the diamond burns away, and it is a direct measure of non-diamond residue. Measured values across high-strength grit span roughly 0.0002% to 0.0093%, a forty-fold range. For bonded tools that spread is irrelevant; for plating, slurry and semiconductor work it decides whether the product passes.
Where The Residue Comes From
Synthetic diamond is grown in a metal catalyst environment, then crushed, milled, cleaned and classified. Each step can leave material behind: catalyst metal from synthesis, mill wear from crushing, and fines from the classification equipment.
Good processing removes most of it. Ash measurement is how you find out whether the processing was good, which is why the number varies between suppliers producing the same nominal grade.
What The Numbers Look Like
| Grade family | Measured ash | Typical concern |
|---|---|---|
| High-strength grit (MBD class) | 0.0002% – 0.0093% depending on size | Low end for plating and clean processes |
| Micron powder (HDY, HDG) | Grade and process dependent | Slurry and optical work |
| Nano powder (HDYM, HDYMC) | Controlled, customisable | HDYMC exists specifically for custom ash requirements |
Two things about this table matter. First, the spread inside one family is real: finer sizes generally carry higher relative ash because surface area is larger. Second, ash value is meaningless without the test method, because different ashing temperatures leave different residues.
When Ash Actually Matters
- Electroplated tools. Non-diamond residue changes plating adhesion and can produce nodules or poor coverage.
- Slurry and CMP. Metal ions in a slurry become electrical defects on a wafer. Wafer work commonly specifies metal content below 10 ppm.
- Thermal composites. The residue sits at the interface you are engineering, and a contaminated interface is a thermal barrier.
- Dental and medical abrasives. Cleanliness requirements follow the application, not the abrasive.
For a saw blade segment, none of this changes the decision. Paying for ultra-low ash in a granite blade buys nothing.
Magnetic Content And Demagnetisation
Synthetic diamond often carries ferromagnetic contamination from the synthesis environment, and some processing steps can leave particles slightly magnetised. In most bonded tools this is harmless. In electroplated tools and in any process handling fine powder, magnetic particles cause clustering: the powder clumps in the bath or on the tool, producing uneven coating and visible defects.
Demagnetisation is a processing step, not a coating. It is specified for applications such as dental burs, plated files and fine plating work, where clustering is the failure mode. If a plated tool shows localised grit clusters, magnetic content is a reasonable first suspect.
How To Specify It
Do not specify “low ash” without a number. Ask for the measured value, the method, and the size at which it was measured. For nano grades, ask whether the ash requirement can be customised, because that is exactly what HDYMC exists to do.
How Magnetic Content Is Actually Measured
There is no single universal number the way there is for ash. Suppliers and laboratories use different approaches: magnetic separation and weighing the attracted fraction, measurement of magnetic susceptibility, or simply a visual inspection of the powder after passing a magnet.
That means a magnetic figure is only comparable between suppliers if the method matches. When a customer specifies “low magnetic content”, the useful follow-up is to ask what the previous supplier measured and how, then request the same test.
For plated tools the practical test is downstream: plate a small batch and look for grit clusters. Clustering under identical plating conditions is a reliable signal that the powder is carrying magnetic contamination, regardless of what any certificate says.
Ash, Colour And Appearance
Yellow and black product families differ in appearance for reasons that have nothing to do with ash, so colour is not a proxy for cleanliness. A dark powder is not necessarily dirtier, and a bright yellow powder is not necessarily clean. Judge by the measured value and the process result, not by the shade in the bag.
Common Mistakes
- Comparing ash between suppliers without the method. Two labs ashing at different temperatures report different numbers on the same powder.
- Assuming finer powder has lower ash. Finer powder has more surface area and often carries higher relative residue.
- Ignoring magnetism until plating fails. Clustering is easier to prevent at purchase than to fix in the bath.
How To Verify
Ask for ash by lot with the method stated, and for a magnetic content figure if the application is plating or slurry. Then confirm against a third-party test once, and use that as the baseline for incoming inspection.
Next Step
Products: HDY, HDYMC custom ash, HDN nano monocrystalline.
Applications: CMP pad conditioners and slurries, electroplated tools.
Related reading: quality control.