When you are searching the web for new and original garden pottery, or maybe the old standby terracotta clay and you see the term "Black Clay" and wonder what exactly that means, then here is the answer!
Many of the garden containers coming out of Vietnam use the term Black Clay. When you look at the photos of the pots they don't look black at all but a dark brown and this causes some confusion. Well let's start by what it really is. Imagine when you are standing at a riverbank in Vietnam and you are looking into the running water and the water looks dark almost black. It's not the water you are seeing it's the soil on the river bed that is a dark brown. Well, when that clay is harvested off the river beds it looks like a dark brown. That is where the term "Black Clay" comes from.
Then the clay is formed into shapes or placed into molds to form the planters. Each one is then moved into a huge mud hut where it is baked over a number of days till hard. When you see some of these planters and they have darker spots on the side that means they were placed closer to the sides of the kiln where they will heat up more than the pots placed in the middle.
The pots are then cooled. And then moved back in and re-fired. This creates a hard finish like a stoneware pot. It's basically waterproof and will wear like a glazed flowerpot. One word of caution. If the pots gets chipped or cracked, the water you water your plant materials with will find that defect and seep into the pot. Now the pot will start to break down from the inside out. This process is normal.
So, hopefully this helps explain where these beautiful clay containers got their name: Black Clay.