Another situation that was perceived by the Sages to be considered ribit (forbidden interest) on a rabbinic level, is a case where someone agrees to a price on a commodity before it is available in the marketplace. According to the Mishna (72b) it is forbidden to set a price for various commodities in advance, out of a concern that once established, the actual market price will be higher than what was paid, a difference that could be perceived as interest, since we might view the lower price as coming in exchange for the early payment. The Mishna teaches, however, that once the commodity exists, it can be paid for, even before a market price has been established for it. Examples of this include a field that is ready for harvest, grapes or olives that have been collected to be pressed, and clay prepared by an artisan.
Our Gemara discusses the artisan’s clay – betzim shel yotzer. Rabbi Meir rules that they have to be fully prepared before they can be paid for; Rabbi Yosei limits that ruling to white clay, but darker clay can be paid for at any time.
An artisan must prepare his clay carefully if he is to produce quality utensils. Raw clay is collected from the ground, broken up and mixed with water. Depending on the desired final product, other materials may be added to it, such as ash, sand, ground up bricks, etc. This mixture is well kneaded and prepared in the shape of balls, which are then dried out. Water is added when the artisan will begin to prepare the utensil. Darker clay is made of the simplest ingredients – clay, perhaps even mixed with ordinary earth – which gives it its color. It is found throughout Israel and is readily available at all times. White clay is made of the finest ingredients and is specially prepared for making unique utensils. This material is found in limited places and is significantly more expensive than the simple clay.