special muffles clay ovens or protective vessels used in assaying which should be cut open only in length, one transverse finger wide at the bottom. Some also use other open-cut muffles, but you will find those which are the best to use for every furnace depicted in the following figure in proper proportion.
Also, for these furnaces, a lid and small sliders made of pottery should be made for the regulation of the fire, as you will hear, whose form is also to be seen in the aforementioned figure.

How one should make muffles, bottom

plates, shards, and other small

pottery belonging to the assaying

process.

It should rightfully be that every assayer, in case of need, can make their own assay furnaces, shards pieces of broken pottery or specialized vessels, crucibles, muffles, and whatever instruments they require daily for the assaying. For one does not find masters in all places who know how to make such things, and even if one often applies much effort to bring the potters to make the necessary tools for the needs of the assaying, it often happens that they make nothing good nor anything well-formed, with which an assayer cannot persist. Therefore I, and many others (where we could not obtain good tools), have often been caused to make such things ourselves, which should then be done as follows.

On the preparation of the clay and what one usually mixes into it.

Take good potter's clay, as good as it is to be obtained, but the clay that is blue and becomes beautiful white in the fire or in the burning is found to be the best to use for this equipment. Let the same potter's clay become quite hard, or dry it in the sun, and when you want to make equipment from it, let the clay be pounded small, and moisten it with water so that it becomes soft; then let it be trodden, or well beaten with an iron, and take under it small ground, levigated refined by washing Kißlingstein a type of quartz or flint, or fine white sand, as much as the clay will endure. But so that you do not add too little or too much, make first of such material,