Co-efficient of Linear Expansion = 9.60
Melting Range = 1450°F
Cone Range: 06-10
This is a popular frit and has been used for many years as a general purpose melter across all tempreatures. Equivalents are made by many frit companies. The manufacturer says that it is "intended for use as a lime and borate source in partially fritted glazes, lead bisilicate glazes and low cost hobby glazes cone 06-10".
The reason this is billed as useful in partially fritted glazes is because of how dissimilar its chemistry is to a typical low fire glaze and the fact that it has a very high thermal expansion (the expansion is because of its lack of alumina coupled with high sodium content, even higher than a feldspar). Interestingly, if alumina is added the thermal expansion drops drastically because there is so much boron to counteract the sodium (this is what Frit 3124 is).
The very high CaO content makes this and similar frits very useful for developing chrome-tin pinks and maroons. CaO sourcing raw materials do not normally melt at low temperatures but a frit of this chemistry (high soda and boron) does.
Unlike raw material sources of the other oxides, this frit has no alumina. Because all glazes (except crystalline) require alumina, this frit must be mixed with a material that sources high alumina. Feldspars are not a normal option because they would supply even more high expansion soda and potash. The only logical answer is clay (normally kaolin). Since crystalline glazes require almost no alumina, this frit is an ideal material on which to build them.
Not many frits have higher boron than this one, so this is considered an excellent source where boron is required but a minimum amount of frit is needed. Since this frit has no alumina adding it to a recipe does not require reduction of clay content to reduce alumina. These reasons are likely why it is billed as useful from 06-10 (although boron is uncommon in high fire glazes).
The high expansion of this frit is quite useful since it can be used in a frit blend to create low-temperature glazes with adjustable thermal expansion. The high boron means it can tolerate a very high alumina content from other materials, especially clay. For example this glaze: 40 Frit 3124, 40 Frit 3134 and 20 Kaolin is expansion adjustable since the Frit 3134 can be increased at the expense of 3124 if the glaze is shivering and vice versa if it is crazing.
This frit is often used as part of the strategy to substitute for Gerstley Borate in glazes. It is valuable because it contains lots of sodium and calcium while at the same time sourcing the B2O3 without alumina. This often enables reducing the feldspar content in the glaze(in addition to eliminating the GB), and then replenishing the oxides contributed by both with this frit. Since this frit contains not alumina, it is possible to add kaolin to supply it, it acts to suspend the glaze in the absence of the Gerstley Borate.
Information from the Digitalfire Ceramic Materials Database