I recently purchased a blue willow ware pattern that is obviously old due to the extensive discoloration and yellowing. (The nature is good for me because I'll be using it in a Wabi-Sabi Tea ceremony in Japan.) It is of high quality, i.e., the pattern is very detailed and has been transferred very cleanly. It has no mark per se but has the number 10 stamped into the clay in the middle of the back. Also the blue is much darker and richer than most blue willow pieces that I have seen, which leads me to believe it was made with an old form of cobalt, the unrefined type that is essentially impossible too obtain these days. (I am a ceramic artist in Japan, where the deep old cobalt color is highly valued.) Can anyone tell me more about this piece?