Gyuto 240mm Full Kasumi Integral Birchbark & Brass


Some bladesmiths emphasise a focus on technical details, some are all about clean lines, others like to focus on technical geometry. While Jonas is certainly always focussed on performance, his work is all about heart and soul. Consider this, the knife featured here has taken approximately a year to produce. Starting in spring 2021 Jonas would have walked out into the local forests surrounding his forge and harvested the Birchbark used in the handle of this knife. He had to store and dry the bark over the summer and artfully select each layer of the handle you see pictured here.

However, that’s only the beginning for a knife like this. Forged San Mai, the steel used for this blade has been pressed together, a sandwich of wrought iron and premium German tool steel forged welded together and then beaten, steel on steel, heat by heat, into the rough shape of a blade. The integral bolster willed into shape with the strike of the hammer. Grinding refines the overall shape of the blade before hours of work on whetstones polishing to produce the Kasumi (mist) finish. That’s a lot of love!

An Isasmedjan knife will grow on you. Rustic certainly doesn’t mean rough, fit and finish is superb. Rather than using the word rustic to describe these knives it would be better to say that they are full of character, charming, with endearing style and class.

As described, this knife features a full Kasumi polish, wrought iron cladding and a very tough, HRC 64+, 1.2419.05 steel core. The handle is a hand harvested birchbark, Rokaku Hanmaru, forged integral with a wrought iron endplate and brass pin.

The profile is Jonas’s classic santoku tipped Gyuto with a decent flat section that gradually settles into a curve towards the tip. The santoku tip gives the knife rigidity, this is not a flexible blade. Stable, satisfyingly weighted, and well balanced. We are not talking workhorse grind though, the knife features a thin, sub 2mm average blade thickness.

Overall, a pleasure to work with on the cutting board.

Between the beautiful birchbark handle and forged integral bolster, the satiny smooth kasumi polish and the artfully crafted performance profile and grind it’s hard to describe this piece as anything short of functional art.

Product Specification

Blade Type: Gyuto

Edge Length: 240mm

Spine Heel: 2.95mm

Spine Mid: 1.98mm

Spine Tip (20mm before): 1.2mm

Blade Height: 52mm

Weight: 234g

Cutting Edge Steel: 1.2419.05

Stainless: No

HRC: 64+

Blade Construction: 3 Layer (San Mai)

Blade Finish: Matte Polish

Grind: Convex

Handle Construction: Hidden Tang

Handle Materials: Hand Harvested Birchbark, Wrought Iron and Brass

Handedness: Ambidextrous

Saya Included: No

Shipping & Returns


We process orders 5 days a week (Monday - Friday) and ship from our shop in Berlin, Germany. We ship with FedEx, UPS and Deutsche Post.

We are happy to offer free international shipping on a variety of orders depending on location and order value. You can check to see where things sit for you here.


At Modern Cooking we want our customers to be inspired and delighted by the products they purchase through our shop.

However, we understand that you may need to return products occasionally. If you are not entirely happy, you can return your purchase in its original condition within 14 days for a refund. Please email if you wish to return any goods.

In the unlikely event that you receive faulty goods or your order is damaged in transit, please contact us for instructions on how to return the goods as in this case we will meet the cost of return postage, though only if this is arranged through our authorised carriers. Any claim for refund or exchange resulting from faulty goods or goods damaged in transit must be raised within 5 business days.

All Modern Cooking logistics partners provide insurance in case of damage, but the coverage is only valid if we are notified within 5 business days. Please make sure to inspect your order immediately upon receipt to ensure that there is no damage.

Once we have the goods back, we will issue a full refund or send replacements where possible, as you prefer.

Product Care:

Cleaning: Clean by hand with warm water. Avoid wetting the handle when possible. 

Sharpening: We advise using whetstones to sharpen your knives and a honing rod or steel to maintain the burr between sharpening sessions. 

Reactive Steels: Reactive steels like Aogami Super, Apex Ultra or one of the many premium reactive German and Swedish steels are susceptible to rust if not properly cared for. In this case we advise that you keep the knife dry between uses and when storing the knife for longer periods wiping the knife blade with Tsubaki oil or another food safe oil is a wise choice. This will not stop a patina forming on the blade, but it will stop rust. A patina can be a beautiful personal feature on your knife and helps to stop rust forming. So, dry your knife regularly between uses, store in a dry place and apply some Tsubaki oil from time to time when storing for long periods. 

A reference guide to steel types

Handle Care: If you have a knife with a non-stabilised wooden handle, you can apply Tsubaki oil or another food safe oil to your handle from time to time. Food safe wax can be applied to both stabilised and no-stabilised wooden handles. Never apply hot wax or oil as you risk warping or damaging the handle.