Green sand is made up of water, clay and sand. According to The Metal Casting, green sand is a top choice for hobby professionals because it is the least expensive and easiest to use. Hobby professionals typically use green sand to create decorative pieces for the home, like sundials and drawer pulls. To create these products, mold green sand into a pattern and then heat the molten metal to be poured into the mold. Molten metal hardens the mold. Heating molten metal can be a challenging and tedious process. Most people use a furnace to heat metal between 1400°F to 1600°F. The molten metal is then poured onto the mold. When the metal freezes, you then have your metal part.
Oil tempered sand contains a binder instead of clay. It is a sand that reacts with oil instead of water. This type of sand is good for high quality metals, and metals that you would to prefer have a very smooth appearance. Oil tempered sand is most often used by experienced professionals; it's usually mixed by a company before the sand casting process. If the wrong type of oil is used, it could interfere with the bonding process, so it is not wise to mix oil tempered sand if you are not a professional. Oil tempered sand is often used to create auto and machine parts.
Core sand, also known as sodium silicate sand, is created by mixing sodium silicate with plain sand and carbon dioxide. This is an inexpensive type of sand used often as a hobby to create decorative pieces such as metal vases. After core sand is mixed, it is used in the same way as green sand.
Resin bonded sand is often referred to by professionals as "no bake" sand, because it will harden at room temperature without heat. Resin bonded sand is created by bonding polymeric resin with silica sand. It often takes longer than other sands in the casting process because the polymeric resin and silica sand have to react. Professionals use resin bonded sand to create metal parts used in the manufacturing and auto industries.
According to The Metal Casting, synthetic sand is "clean, graded sand in which clay can be added as desired." Synthetic sand allows professionals to control its strength by adding as much or as little clay as necessary. Otherwise, this sand is used the same way green sand is used.