Delicas are a particular bead manufactured by world renowned Miyuki, Japan's oldest seed bead producer. They are cylindrical in shape with a large hole that allows multiple passes of thread through each bead and are available in a large selection of colors and finishes.
Size 11 is the most popular size of the Delica beads with 944 varieties of colors, finishes and treatments in the round cylinders plus another 55 in the hex cuts, which are hexagon shaped cylinders. The diverse variations are produced by particular glass treatments. There is basic transparent glass, basic opaque glass, and etched glass for a matte or semi-matte effect. Then there are the various colored glasses.
Additionally there is a variety of finishes or treatments. "Treatment" refers to something that is done on the surface of the glass and can be on the top, at times within the hole and sometimes one finish on the top and a different finish in the hole. Treatments can be made up of a clear "rainbow" or "aurora borealis" finish, a "pearl" finish, colored dyes, as well as many types of metal coatings such as precious metals. Some Delica beads have more than one treatment applied to them in order to result in the desired effect.
Be aware that there are some durability concerns with a number of the finishes such as the dyed or galvanized beads. The best suppliers will be able to supply you with the durability information.
Miyuki also manufactures a size 10 Delica that is somewhat bigger, a size 8 that is a lot larger than the size 11, and a size 15 that is a lot smaller. The size 10 and 15 are relatively new and as a result don't come in as many colors and finishes as the size 11.
Miyuki's Delica beads are of very high quality and as a result they are more expensive. You should buy them from a reliable bead retailer that sells the true article. You should be aware that some suppliers have been known to buy cheaper, lower quality beads from another manufacturer and pass them off as Delicas. Also be very wary if you are tempted to buy at an on-line auction.
If you are buying your beads to complete a pattern that gives you the Delica number, such as DB-010, you shouldn't have a problem due to the fact that each color has a number. But if you are getting your beads by description you likely will have a problem, due to the fact that there is not a standard color description for each bead. The reason being that the Japanese description does not translate readily into English and the different importers each have their own interpretation. So it's always best to go by the DB- number.
Real Delica beads are a superb choice in any Loom, Peyote or Brick project due to the fact that they are so regular. They make any pattern line up perfectly and give a clean, crisp finish to your beadwork. There are fewer culls when you are working and therefore they are more cost effective than their price might indicate. And the color and finish selection is fantastic!