Nubatama Ume #25 (XXXC Black Aratae)

Why You Need This Stone: The #25 grit is an extra-extra-extra coarse (XXXC) abrasive designed for severe metal removal, heavy reprofiling, and major edge restoration. Operating as a modern, hard-wearing interpretation of a traditional Japanese Aratae (rough stone), the Ume #25 allows you to reshape damaged blades and remove deep chips rapidly on a bench stone, bypassing the need for power grinders that risk overheating the steel's temper. Formulated in a 50mm brick profile for extended shop life.

Buy This Stone If:

• You need to repair major edge chips, broken tips, or severely damaged geometries.
• You are performing heavy thinning on thick blades or reprofiling primary bevels from scratch.
• You want an extremely aggressive, fast-cutting coarse stone sourced from the Ken Schwartz Estate collection.

Specifications

• Brand: Nubatama
• Grit: #25 (Extra-Extra-Extra Coarse / XXXC)
• Series: Ume (Black Aratae)
• Type: Soaking / Semi-Soaking
• Dimensions / Profile: 210 x 75 x 50mm Brick
• Binder Hardness: Medium-Hard
• Provenance: Ken Schwartz Estate

Notes & Usage

• Common Tasks:
  • Grinding out deep edge chips, broken tips, and severe blade geometry damage.
  • Heavy thinning behind the edge on thick, unmaintained kitchen or shop tools.
  • Rapidly resetting bevel angles before transitioning to a standard coarse stone.
• Cutting Action & Speed: Utilizes large, highly aggressive silicon carbide grit particles to shear through steel rapidly. It creates a coarse, dark slurry that accelerates material removal while keeping the cut consistent.
• Surface Feedback: Very tactile with an aggressive, audible "bite." The stone provides immediate feedback on high spots along the bevel.
• Steel Compatibility: Works across almost all metal types, including tough stainless alloys, carbon steels, and hard tool steels.

Progression Ideas

• Preceding Step (Lower Grit): None (this is typically the coarsest bench stone step available in a hand-sharpening setup).
• Following Step (Higher Grit): Nubatama Ume #120 or Bamboo #150 (to erase the extremely coarse #25 scratch pattern before moving to medium repair grit).

Also Consider

• For Moderate Repair Work: If you only need to fix light chips or perform routine edge restoration, consider a milder coarse stone like the Nubatama Ume #120 or Bamboo #320.
• Essential Maintenance: Because of the large grit size, keep a heavy-duty coarse flattening plate or dressing stone nearby to refresh the surface and maintain flatness during heavy grinding sessions.

Condition

New in original factory box and packaging. Due to long-term storage (5+ years), outer boxes and paper wrapping may show minor shelf wear or scuffing.

Note: Photos represent our stock inventory for this stone; individual box wear or color tone may vary slightly from the unit pictured. Reference objects (rulers, coins) are for scale only and are not included.