This is a popular frit and has been used for many years as a general purpose melter across all temperatures. Equivalents are made by many frit companies. Ferro says that it is "intended for use as a lime and borate source in partially fritted glazes, lead bi-silicate glazes and low cost hobby glazes cone 06-10". But from the viewpoint of ceramic chemistry, this frit is a great 'oxide warehouse', it is useful in so many kinds of glazes, we often use it to showcase the value of Frits in formulating and adjusting glazes as (formulas of oxides rather than recipes of materials).
The reason this is billed as useful in partially fritted glazes is because of how valuable it is in supplying B2O3 (raw B2O3 sources have many issues). It gives us lots of boron along with CaO and Na2O (which most glazes need) but no Al2O3 (so it can be supplied from clay to harden and suspend the slurry).
Several factors make this frit's chemistry so attractive:
-It has almost no alumina. That means, as already stated, that Al2O3 can be supplied by clay, giving the glaze better suspension and hardening properties. Conversely, adding Frit 3134 to a recipe (to supply boron for example) does not require reduction of clay content.
-It has high sodium. That means that it's presence enables reducing feldspar content which in turn provides even more opportunity to source Al2O3 from kaolin or clay.
-It has high boron. That gives it a lot of bang-for-buck as a flux, especially in middle temperature.
-It has a very high CaO content. That makes it 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.
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, 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 effectively 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. This often enables reducing the feldspar content in the glaze, and then replenishing the oxides contributed by both it and the GB with this frit and kaolin (the latter of which acts to suspend and harden the glaze slurry).
Since Frit 3134 contains no Al2O3, it is not a completely stable glass, it can dissolve in glaze slurries over time and precipitate (to turn the water brown). It is often possible to reduce its amount in favor of the more balanced Frit 3124 (where the glaze has significant feldspar). However, if you drive the clay content too low to accommodate the Al2O3-containing Frit 3124 (using glaze chemistry), you may find the extra hassle of poorer application properties and powdering worth enduring some precipitation issues.
60% Frit 3134 & 40% Frit 4131 is used to replace Frit 4108