You’ve mastered the basics, and now you’re ready to dive in. Written by Twigg in Toronto, this article serves as a basic explanation for every type of whetstone (sharpening stone), all the brands we carry at Knifewear, and what they’re good for. Twigg is a major sharpening nerd, so he made sure to translate things so they’d be easy to understand.

Types of Bonds 

Magnesia Based (WTF is that?)

Magnesia-based whetstones use magnesium oxide as a cement-like binder to hold abrasive particles together, offering an exceptionally crisp sharpening feel, fast cutting speed, and high density. 

Key Characteristics

• Splash-and-Go: Most magnesia stones require no soaking. You only need to splash water on the surface before use.
• No Soaking: Never submerge magnesia stones in water for long periods. Prolonged water exposure can break down the magnesium bond and ruin the stone.
• Surface Appearance: They can develop fine hairline cracks or pockmarks as they cure and dry. This is normal for cement-like binders and does not affect performance.
• Maintenance: They are hard and wear slowly, but can be more brittle than resin or vitrified stones.

Vitrified Bond (uh, what?)

A vitrified bond is a glass-like bonding material used to hold abrasive grains together in grinding wheels. It is created by fusing clays and fluxes at very high temperatures.

Key Characteristics

• Material: Made from clay and ceramic substances fused together like glass.
• Strength: Creates a very strong and rigid structure.
• Porous: Helps clear away tiny metal pieces
• Soaking: Required

Resinoid

Since resinoid whetstones are made by aging at a low temperature, their elastic forces are high. We don’t need to soak them in water before using them, so we can start to sharpen knives with them immediately.

Key Characteristics

• Resin Binder: The abrasive particles (like aluminum oxide or silicon carbide) are mixed with resin and cured at a low temperature around 200°C.
• Splash-and-Go: Most resinoid stones do not absorb much water, meaning they are ready to use with a quick splash or spray rather than a long soak.
• Fast Cutting & Mud: They tend to be softer and wear down faster, releasing fresh abrasive particles quickly to create an active sharpening mud and a smooth finish.

Why would I want a soft/hard whetstone?

Soft Whetstones

• Slurry production: Wears down quickly to release fresh abrasive grains, creating a muddy layer (slurry) that speeds up metal removal. Though great for knife finishes, the slurry can impact deburring. Edge maintenance without proper fundamentals might lead to gouging the stone.
• Preparation: Often requires soaking in water before use.
• Maintenance: Dishes (develops a hollow surface) faster and needs frequent flattening.
• Best used for: Difficult-to-grind or high-alloy steels, since continuous grit release prevents the stone from glazing over. 

Hard Whetstones

• Slurry production: Holds abrasive particles tightly, releasing very little material and remaining flat much longer. Generally not great for final knife finishes, but very useful when bevel sharpening when you want the shinogi to be very flat.
• Preparation: Frequently designed as "splash-and-go" stones that only need surface water rather than a long soak.
• Maintenance: Maintains its flat surface profile over extended sharpening sessions.
• Best used for: Everyday touch-ups, polishing, and softer or easier-to-grind carbon steels.