Because it is a coating, and a coating is a surface. Powder coat is baked onto the iron as a dry film and it holds well, but it sits on top of the metal rather than being part of it. Give it years of dishwasher cycles and it will eventually lift at an edge and work outwards from there. The base underneath is still iron and still sound. What you lose is the finish, not the dish.
What powder coating is, and why we used it
It is not paint out of a tin. The colour goes on as a dry powder, the part is charged so the powder clings to it, and then it is baked until it flows into one continuous skin. That skin is far tougher than sprayed paint and it does not chip from a knock the way enamel does.
It is also the reason the dish can be a colour at all. Bare iron is grey, and a butter dish that lives on a counter is a piece of furniture as much as it is a container.
Why it lifts
Three things, in the order that matters:
Heat and time. Every dishwasher cycle is a heat cycle, and iron and the coating expand at slightly different rates. Each cycle is nothing. Two hundred of them is a slow, repeated stress at the edges, where the film is thinnest and where it has an edge to peel from.
An opening. Coating almost never fails in the middle of a flat face. It fails where something gave it a start: a scrape from a knife stored in the dish, a chip from a corner meeting a tile floor, a rim that took a knock. Once water is under the film, the lifting has somewhere to go.
Salt and fat. Butter is salty and salt water is patient. Left to dry in a corner rather than rinsed away, it works at any opening that is already there.
What to do about it
To slow it down, wash the base by hand and dry it. Keep knives out of the dish between uses. Rinse rather than wipe when butter has been sitting.
Once a patch has lifted, there is no honest repair. Touch-up paint will not bond to a baked powder film and it will not match. What you can do is stop it spreading: dry that spot every time, and keep the dish out of the dishwasher from then on.
Bare iron where the coating has gone is not a hygiene problem. It is stainless underneath, and stainless does not need a coating to be safe against food. It is a cosmetic problem, and whether that matters is your call rather than ours.
What our customers say, including the ones who mind
This is the most common complaint on the butter dish, and it is the reason its rating sits where it does rather than higher. Amazon's own summary of the reviews says it plainly: several customers report the coating peeling off over time.
One of them, who stayed with us anyway, wrote:
This is my second purchase of this butter dish. I love that it is durable on the counter compared to ceramic, and that the bamboo top fits well. The paint delaminated after a few years, but I liked it enough to get another. I washed the base in the dishwasher every month or so, hand washed the lid and gasket.
A few years, with monthly dishwasher cycles, is roughly what this finish is good for. We would rather publish that number than let you discover it.
The honest limit
A coated dish will always be a dish with a wear layer on it. If you want a butter keeper that cannot lose its finish, you want unfinished stainless or you want ceramic, and both come with their own trade: one is grey, the other breaks.
We chose powder coat because the alternative to a coating on a counter object is either no colour or a material that does not survive being knocked off a worktop. That is the trade, stated as a trade.
What is covered
The butter dish carries a two-year guarantee against manufacturing faults. Coating that lifts within that window, without an impact to explain it, is a fault and we will replace the dish. Coating worn through after years of dishwasher use is the surface doing what a surface does, and it is not a claim.
If you are not sure which one you have, send a photo and your order number to help@kensingtonlondon.com and we will tell you honestly which it is.