Why ware changes the cup
Red tea, called black tea in the West, is fully oxidised and therefore the most tolerant of heat. It wants 90 to 95 degrees and it will survive a full boil without much complaint.
That tolerance means ware matters less for temperature and more for two other things: whether you can remove the leaf, and whether the vessel holds enough volume for a proper dose.
Fully oxidised leaf gives up its compounds quickly and completely. Once it has done so, anything further is astringency rather than flavour, so the leaf has to come out.
The fourth consideration is that red tea is often brewed Western style in a larger pot. That changes the geometry, because a tall narrow pot brews differently from a wide shallow one.
A third factor is that red tea is usually brewed once rather than repeatedly. That favours a vessel sized for one full cup over the small multi steep ware the Chinese categories prefer.
The oxidised leaf also holds its colour, so a clear vessel is not required. You can judge a red tea by aroma and taste alone, which widens your options considerably.
Best ware for Red tea
A 200 to 300 millilitre porcelain teapot with a removable basket is the practical everyday choice. Five grams, water at 95 degrees, four minutes, then lift the basket out.
A porcelain gaiwan of 120 millilitres is better when you want to drink it Chinese style. Five grams, boiling water, 15 seconds, and it will run six or seven steeps.
Glass is fine and has the advantage of showing the liquor, which is useful because red tea should be clear. Cloudiness as it cools is normal and not a fault.
Clay works for the malty, strong origins such as Assam and Keemun, where retained heat helps rather than hurts.
If you take it with milk, use a pot large enough to brew strong. A weak brew with milk is the most common failure here, and it is a volume problem rather than a ware problem.
A stainless steel mesh basket inside a ceramic pot is a good compromise. It gives you the larger volume red tea wants and it lifts out cleanly, which are the two things that matter.
For iced red tea, brew double strength and pour it over ice. Ten grams in 500 millilitres for four minutes, then into a jug of ice, keeps the liquor from going watery.
What to avoid
Avoid leaving the leaf in the pot. This is the single biggest mistake with red tea, and it turns a good tea astringent within five minutes of the steep finishing.
Avoid small doses in large pots. Red tea needs 5 grams per 200 millilitres, and halving that gives you coloured water however long you wait.
Avoid porous clay for the delicate origins such as Darjeeling first flush. The muscatel note is fragile and clay will blunt it.
Avoid an insulated flask for a long steep. Red tea tolerates heat better than green, but eight hours on the leaf still produces something harsh.
Avoid narrow necked pots. Red tea produces small leaf fragments that clog a narrow spout, which slows the pour and over extracts the last of the liquor.
Avoid very small cups for a Western style brew. A 200 millilitre mug cools slowly enough to stay pleasant, and it matches the volume you actually brewed.
The one rule
Pick ware that lets you remove the leaf at the right moment. Everything else about red tea is forgiving, and this one thing is not.
When the cup is astringent, shorten the steep before you lower the temperature. Red tea rarely fails because the water was too hot.
When it is thin, raise the dose rather than the time. An extra gram does more than an extra minute, and it does not bring the astringency with it.
Red tea is the category where good habits matter more than good equipment. A cheap pot with a basket you actually use beats an expensive one without.
One test: brew 5 grams for four minutes and taste it, then brew the same dose for six. The second cup will be stronger but not better, which is where red tea tops out.