The main sins are short blades and obese blade stock. There also tend to be issues with the grind, but those are minor in comparison to the more fundamental problem of squatty, fat blades that are either too short to slice properly or are so fat that they wedge what you're cutting apart. Or most often, both. Overall blade shape can also be an issue, but again... the main problem is that people make knives that are too short and too thick to be of general culinary use. Sadly, many of these complaints apply to the Spydiechef, which is a fantastic knife for bleeding and gutting fish (like a small, rust-free pocket deba) but isn't a very good all-around knife for food prep (IMO).
Let's start with blade length. To get the ball rolling, here are some of my smaller kitchen knives:
From top to bottom, that's a 150mm Yoshihiro AS petty, a 105mm Yamashin White #1 tall petty, a Misono UX10 120mm petty, a 4" serrated Spyderco utility knife, and a Kuhn Rikon Colori "paring knife."
The top two knives are basically there for comparison purposes. 150mm is still very much a small kitchen knife, but it's freaking huge by folding knife standards. Obviously, that's out. The 105mm tall petty is a fantastic knife for mincing chives, garlic, shallots, ginger... the extra height allows it to function like a larger knife in many respects, since you get a lot of added board clearance. But making a tall petty into a folder would create a gigantic pocket monster that's too thick to carry comfortably. In my experience, 120mm is about as short as you can go on a petty knife and still have it be useful for board work. The Misono UX10 hits the real sweet spot for me. It's not overly tall, but it's long and thin enough that you can do an astonishing number of tasks with it. I used it to break down several turkeys this holiday season -- and actually preferred it to my honesuki, which was surprising. The Spyderco and Kuhn Rikon knives are excellent fruit knives. I got the Spyderco for Christmas, and mowed through a case of clementines for juice the next morning. The KR is carried by a lot of bartenders, and is great in a lunchbox. But they're a little too short for proper board work.
So here's the thing about length. Once a kitchen knife shrinks below 120mm, most companies stop marketing it as a petty and start calling it a paring knife. Paring knives are meant for off-board work, like peeling things or turning mushrooms or carrots into Frenchy shapes, rather than slicing and dicing. They live in your hand, and seldom if ever touch a cutting board. You can get a bit shorter than 120mm and call it a non-paring knife, like the Spyderco small "utility" knife or the KR "paring" knife. These aren't great subsitutes for true paring knives (which are even shorter) but are okay for cutting very small produce. They are still too small to cut through things much bigger than a lemon. If an orange can threaten to overwhelm your knife, your knife isn't a great all-arounder in the kitchen. (Sorry, Spydiechef. If only you were 50% larger... and thinner... and had less of a belly... who's rock chopping with a folding knife anyway? But I digress...) With the issue of length in mind, here are some of my longer folders next to the Misono.
From top to bottom, that's the Extrema Ratio Dark Talon, Misono UX10, ER Resolza, Spyderco Pattada, and an Opinel slimline 10 and 12.
The Dark Talon is so close to what I'm looking for. It flirts with being a folding 120mm petty, and the wharny blade shape makes chopping easy (no rocking necessary... just come straight down). The stabby tip is great for delicate work. The Resolza is also lovely, but the blade shape isn't really great for board work (though it may be the best letter opener around... sorry Sal!). The Pattada's blade shape also doesn't make it great for cutting on a board, but my main issues with it are that it's too short and too fat for food prep. I love the Pattada. Love. Just not for this task. The Opinels are sufficiently long, but insufficiently tall for food prep. They also border on too thin, which gives the blades more flex than you'd want in a kitchen knife. They're awesome steak knives though. Because of their thin blade stock, the Opinels run circles around everything else in terms of slicing ability. It's almost embarrassing, considering how cheap they are.
This brings me to the issue of girth. It's hard to get a great comparison shot, but here goes...
TTB: Resolza, Pattada, Dark Talon, Opinel, Misono UX10, Spyderco utility knife.
The Pattada's 3.5mm thick blade stock is absurdly thick by kitchen standards. Maybe not by Taktikal Knife Bro standards, but by kitchen standards it's a thickass knife. I cut an apple with it once and it made me want to kill myself. Halfway through the slice, the wedging was so much that the apple slices were splitting and cracking. I say this with love, since I LOVE THE PATTADA. Just not in the kitchen. The more slender Extrema Ratios are still too thick, which is a shame for my purposes. The dicing onions can get messy as the fat top of the blade pushes the different layers apart when you come down through the product. I had similar issues with the Spydiechef; full flat grinds are nice, but they can't compensate for steel that's 3mm thick. The Opinels are super thin -- too thin for real kitchen purposes. They're much thinner than either the Misono or the Spyderco utility knife, which are themselves much thinner than your ordinary upscale folders.
I suspect that problems with girth stem from the fact that many modern locking mechanisms require thick blade stock for secure lockup. You've gotta have a few millimeters of steel for liner locks or RILs or whatever else to click into. All that's fine and good. But what would be interesting to see is something that's thick in the lock but IMMEDIATELY thinned out as soon as the blade starts. By way of analogy to non-folding kitchen knives, many of the san mai blades made by Katsushige Anryu are very thick at the handle, but thin out extremely fast in the first inch or so of the knife (where the blade actually starts) and hold a thinner profile for the length of the blade. This is most dramatic on my nakiri, but all of my knives from him exhibit similarly thick blade stock near the handle:
The spine starts out quite chunky (3.5mm+) but drops where the blade starts. The idea on the folder would be to keep the blade stock in the handle thick (3+mm) but have the part that extends beyond the handle be radically thinner. Keep it thick around the pivot, but thin it down a lot where the blade actually is. I don't know if that's feasible or desirable from an engineering standpoint, but it sure seems desirable from the standpoint of actually cutting food. Distal taper and thinner grinds can only do so much if you're starting from a thick chunk of steel. Alternatively, maybe it'd be better to start with thinner blade stock and use different styles of lock that depend less on blade thickness. I have no idea. I know precious little about folders.
Anyway, I'm still on the search for something that's long enough, thin enough, and sturdy enough to actually want to use in a kitchen. If such a knife exists, let me find it. If it doesn't exist, let them make it - long, lean, and slicey. Minimal belly. Some nice distal taper. In LC200N so it won't rust when you wash it...
A man can dream.
