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. Ferro 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". 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). 

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.