Coil pitchers

Last spring I made three coil pitchers for fun and then the summer pottery hiatus meant they languished on the shelf until last week, when I finally finished them. That is to say I finished two of the three, the smallest one was knocked off the shelf by a cat and plunged to its death in August or September. No great loss really. I decided to play around with under-glaze to finish the other two, so the red and green tops are painted on the bisque, and then clear glaze applied to the whole thing inside and out. Even though I put two layers of clear glaze on the inside and outside, I find that water still leaches through the bottom where there is no glaze on the outside. It may be because they are coil constructed pots, but I think it is more likely the result of under firing the glaze. I made other water tight pots by the coil method before, I have two functional tea pots made this way, and I don't actually coil the bottom, but I use a slab bottom so it should be leak proof. I know I under fired these pots, because I couldn't see the witness cone very well inside the kiln as it was firing, and as I had over fired the previous kiln, when the temperature reached 2160, I left it for 10 minutes and then shut it down. I thought I could see that the cone had dropped, but I was mistaken, the cone 5 was just starting to bend. These are made of my speckled clay, but they are not as speckled as some other things I have, and this may be another result of under firing too.
The seeping water is really very little, and I wouldn't notice it except I left the green pitcher full of water on the studio table that is covered in canvas and when I went to move it is was damp underneath. The red pitcher is on the wood stove to add moisture to air. Last year we used a crock pot from China Town for this, and it eventually marked the stove with rust where it leached too. Eventually I may get around to re-glazing and re-firing these pots to see if that makes the difference.