The idea, which is the same in every version
One vessel holds a very strong brewed concentrate. Another holds hot water. A glass is filled part-way with concentrate and topped up with water, and how much of each is a per-person choice made at the moment of pouring. The advantages are practical rather than aesthetic. Tea can be offered to anybody at any time without brewing a fresh pot. Everyone gets the strength they want from one preparation. And the concentrate does not spoil the way a standing pot of ordinary-strength tea does, because it is being kept hot and is diluted at the point of use. This is the dominant serving architecture across an enormous area — Russia and the former Soviet space, Iran, Turkey, Azerbaijan, Central Asia and parts of the Middle East — and it is almost invisible in English-language tea writing, which is organised around the single Western pot.
The samovar
TeaHQ's own reading of well-attested general knowledge, with no single source behind it.
A metal urn with an internal heating element — historically a vertical chimney burning charcoal or pine cones, now usually electric — holding several litres of water at or near the boil, with a tap at the front. On top sits a small teapot, the zavarnik, kept warm by the rising heat and holding the concentrated brew. A glass gets a splash from the small pot and is topped from the tap. Russian service adds its own conventions: the glass frequently sits in a podstakannik, a metal holder that makes a hot glass handleable, and tea is drunk with jam, sugar held in the mouth, or lemon. The samovar as a piece of furniture is a social centre — it stays hot, so somebody is always able to be offered tea, and that is the point of it. The Iranian version is closely related and equally central to hospitality, with its own service conventions and its own habit of drinking through a sugar lump.
The çaydanlık
Turkey's version stacks rather than sits alongside: two kettles, one on top of the other. The lower holds boiling water; the upper, narrower one holds leaf and water and brews over the steam, so the concentrate is heated gently and continuously without being boiled hard. The tea is poured from the upper pot into a small tulip-shaped glass — the ince belli, waisted so it can be held by the rim without burning the fingers — and diluted from the lower. The dilution is named and requested: açık for weak, koyu for strong, and a host will ask. The glass shape is not decoration either. Clear glass displays the colour, which is how strength is judged, and the waist keeps the fingers away from the hottest part. Moroccan practice is a third variant of the same principle by a different route: the brew is strengthened and aerated by repeated pouring rather than by a second vessel, and the long pour from a height is doing work rather than performing.
How to do it without the equipment
The principle transfers to any kitchen and it is genuinely useful for a household where people want different strengths or drink at different times. Brew a concentrate at roughly three to four times normal strength in a small pot — more leaf, not longer time, for the reasons the extraction guide gives. Keep a kettle or flask of hot water beside it. Pour an inch of concentrate into a mug and top up. Keep the concentrate hot rather than letting it stand cold, and make it in a quantity you will finish that day. Black tea suits this best; it is what every tradition using the method drinks. Delicate green teas do not — they do not take well to being held hot, and the method was not built for them.
Why the single Western pot is the odd one out
A Western pot brews to a single strength for everybody and starts deteriorating from the moment it is poured, which is why British practice developed the tea cosy, the habit of topping up with hot water, and a certain amount of resignation about the third cup. The two-vessel systems solve that structurally rather than by accepting it. That is worth noticing, because tea writing tends to present the Western pot as the default and everything else as a curiosity, and on this particular problem the default is the weaker design.