The most common question that is asked by someone who is new to the design and modeling field is, what is the best clay to use for my scale model? The answer to this depends on where you are in the world, as you can imagine different cultures have different views on what is best for them. From what I understand there are a few companies that are prevalent for the use in automotive design, Chavant, Faber and Kolb are the ones that I am familiar with.
Here in the United States it is common to use the material that is manufactured here, i.e. Chavant This material is manufactured in New Jersey and they have over 100 years of experience to pool on. There are two categories of clay, fine arts and industrial. The fine arts material is favored by free form sculptors such as special effect modelers and motion picture specialists. These clays tend to be softer than the industrial types and can normally be used at room temperature with no additional warming needed.
The industrial clays are harder and a warming oven is required to bring the clay up to a working temperature but once applied the clay is then worked with specialized tools to develop the design. These industrial clays come in various degrees of hardness, that is they still require warming but the hardness factor differs depending on the type you use.
In Europe a commonly used industrial clay is Faber. As with the Chavant clay this also needs to be heated in an oven to bring it to a workable temperature. The difference with this clay is it is sulphur free therefore has less of a smell compared to Chavant, even so chavant does manufacture a sulphur free clay.
Another product from Germany is Kolb clay. As with all industrial clays it needs to be heated in a warming oven to make it workable. Once it has cooled down it becomes hard enough to progress with your design. Each of these clays have their own merits for using them, it is normally the case of availability. Once again this is an odourless material that does not oxidize with age.
With all of these industrial clays, they are all suitable for use with modern milling equipment, such as the Tarus Clay Milling Machine, but equally, they are also at home with traditional hand tools as well.