Ceramic beads are beads that are made from clay and then baked in a ceramics oven called a kiln.  Ceramic beads include porcelain beads and raku beads.  Clay beads have been made and traded for 3000 BC.  Early beads were made of clay and left to harden in the sun.  

Ceramic beads can be made by hand and therefore made in any size, form or style.  Some of them can be very rustic: hand-formed with the inclusion of sand, dirt, pebbles or sticks and include fibers, such as fur.  On the other side of the spectrum, porcelain beads can be made with slip, a liquid clay, that is poured into a mold, left to dry, removed from the mold, painted, fired at a very high heat, cooled, glazed and fired again.  

Most often, beads are made from earthenware.  Earthenware is made from clay out of the earth, so it is the same color as you find it in the earth.  Nothing like Play-Doh.  I grew up where the soil was considered really bad because it was full of clay.  Takes the fun out of serious gardening.  We'd curse the clay when we had to dig a hole to plant a tree or bury a pet.  Sometimes clay in its natural state has more of a reddish brown tone or greenish gray hue, depending on the minerals in the soil.  The more iron, the more red. 

Once the clay is formed into beads, it is fired to reach a certain temperature, generally somewhere between 1,000 and 1,200 degree.  This bakes out all of the moisture, so it is a little rough.  Stoneware is more smooth than earthenware.  It is fired between 1,100 and 1,400.  

Porcelain is typically a light gray or white clay.  It contains crystals and minerals, such as quartz, silica and feldspar.  It is fired from 1,200 to 1,400 and is very dense and durable.  If you want to make a very refined bead with a lot of detail, it is best to go with porcelain beads as their surface is very hard and smooth, not porous.  

Raku is a type of ceramic that originated in Japan.  It is fired in a different way.  Whereas earthenware, stoneware and porcelain are placed in the kiln and the kiln is then slowly heated to the optimal temperature over a long period of several or many hours, Raku is fired quickly in a fraction of the time.  More like minutes instead of overnight.  Other ceramics are left to cool in the kiln, but not Raku ceramicists.  They are grabbing those beads while they are still burning hot.  I knew a great Raku artist who would put his beautiful clay creations packed in newspaper in a old-time metal trash can and then light it on fire, put the lid on and wait.  After the fire went out, he'd remove everything and it would have this fantastic mottled, smoldered finish.  The chemicals in the glaze would do their own wacky, wonderful thing and the unglazed areas would be black.