Understanding Mesh Sizes for Gilsonite Powder

“200 mesh” and “600 mesh” appear on almost every gilsonite specification. Here is what these numbers mean and why they matter.

What mesh means

Mesh is the number of openings per linear inch in a sieve. A 200-mesh sieve has 200 openings per inch, each about 75 microns wide. If gilsonite passes a 200-mesh sieve, its particles are smaller than about 75 µm.

Common sizes

Why particle size matters

• Drilling fluids: particle size should match pore and fracture sizes for effective sealing.
• Cementing: medium sizes give good slurry properties.
• Inks and paints: fine particles dissolve or disperse faster and give a smoother finish.
• Foundry: size affects how quickly volatile gases are released.

How it is specified

A specification usually states the percentage passing a given sieve, for example “95% passing 200 mesh”. Laser diffraction can also give D50 and D90 values.

Choosing a grade

Finer grades require more milling energy and cost more. Use the coarsest size that works. For inks and coatings, our micronized gilsonite offers 300–600 mesh. For drilling and asphalt, 200 mesh powder is standard.