What is a charger? Why did the Ming dynasty like blue and white so much?
A charger is a decorative plate used in formal dinner services. It is placed underneath the plate one eats from, so it adds a splash of color or design that isn't coming into contact with food. "Charger" is also used to refer to any plate that is too large for a single person. Chargers were used as serving plates in a number of cultures, and in the Middle East were used communally. Blue and white porcelains became popular for Chinese audiences during the Ming dynasty. In previous times, blue-and-whites were more popular as an export. The appeal of the color at the time was the same as today, people really liked it! Additionally, cobalt was one of the only bright colors that you could apply under the glaze. Other colors would burn up in the glaze firing, so they had to be added on top of the glaze, which meant they chipped off easily.
Why is the blue on these different than on other Chinese ceramics I’ve seen?
As far at the plates: I believe the difference in color is simply a result of different ratio of chemicals in the pigment. My understanding is that Chinese potters at the time were striving for that same brilliant blue every time.