The two mugs are thinly potted, well proportioned (both pretty to look at and well-shaped to limit heat-loss through surface evaporation), light-weight (easy to lift, don't take too much heat out of the tea), and they fit my hand perfectly (they are five-fingers-high and just the right width for my hand to wrap around comfortably). They take about 200 ml of tea, which is about the right serving for my body-size (and appetite). The fluted opening assures that the edge remains cool, allowing one to lift them (as one lifts Asian cups -- by the edge) without burning one's fingers.
The first one is matte. I have yet to research this type of glaze.
It's certainly very pretty: mildewed reeds in early autumn. This cup is especially pretty inside:
even though, personally, I prefer cups with white or light-colored glazing inside as they allow one to see the color of the tea. (This is not only pleasant, but also has the practical benefit of allowing one to judge whether the tea is strong enough).
The second cup is glossy-glazed. The outside glaze is called robin's egg: the glaze contains a mixture of two different salts which melt at slightly different temperatures and separate in the kiln, creating tiny, milkish runs in a dark-blue background.
This is not the best robin's egg I have seen, or even the best I own, but it is the best robin's egg I own on a cup which is comfortable to drink from. This glaze is famously difficult to fire: out of 10,000 cups perhaps 2 or 3 might be "perfect" (and command huge prices). Finding a piece which has both the right shape and a well-executed robin-egg is very difficult.
The inside is glazed in a different color: a kind of blond caramel. This, too, has run revealing finger marks on the inside of the cup (the cup was thrown on a wheel). They seem to me like the ribs of the great behemoth -- seen from inside the belly.
I like containers with a strong color contrast between inside and outside. And the caramel color is light enough to allow me to see the color of my tea.
I have declared these two cups to be a set: similar enough to be a set, yet different enough to be interesting. I like to mis-match my pottery this way: uniform sets testify to the aesthetic laziness of the host.
I'll serve you your tea in them when you come. By the side of my pond, of course (small ponds being, as you know, the perfect place to have tea, especially if there is a small wooden bridge nearby, or a small painted wooden boat; or so says a Chinese classic, the Chasu).
Here I have them all: the pond, the bridge, the boat, and the tea.
The Platonic question as to whether there are universal values has herein its answer: some cups are better than others. A cup must be not too large (or one can't finish the tea) and not too small (or one is kept busy rebrewing and refilling); it must be of a shape that fits one's hand well; and shape and thickness which won't cool the tea excessively; it should be white or light-colored inside to allow one to evaluate (and enjoy) the color of the tea.
Thus a goodness of an object can be shown to depend on the use to which it is put. It is very well for someone to say "I prefer that cup over this", but what if he is not a tea-drinker? Then, in a certain sense, his opinion is irrelevant and his cup is probably useless -- for tea.
Similarly with glazes: as one learns about the techniques and looks at different pieces executed in it one learns to recognize quality -- the difficulty of the piece and the excellence (or not) of its execution: a connoisseur is only as good as the sum total of everything he has seen. It's hard to say that a robin's egg is better than a celadon; but it is quite easy (and uncontroversial) to say that this robin's egg is better than that. And thus under certain circumstances one may well say that this robin's egg (a rare, well executed robin's egg) is better than that celadon (a badly executed celadon). In this sense it is true that quality is relative; but not in the sense in which the phrase is usually meant: there is nothing arbitrary about the goodness, only the initial conditions are. (E.g. shall we have a tea cup in robin's egg? If so, which one will do best?)
Thus it can be seen that there are true value judgments: they are true within a context. It's a little like the direction in which you point your car: north is the good direction if that is in fact where your destination lies. But if that is where your destination lies, no other direction will do.