Flux
Flux means “flow” in Latin and that’s exactly what it does—allows solder to flow on the surface of the silver. Mainly it keeps the heated silver from oxidizing which would keep the parts from sticking together properly. Like everything else the early smiths used, it is found naturally in the area. It is primarily borax, an alkaline salt, sodium borate. Another flux is potassium nitrate. Both can be found around deposits of potash which are fairly common in the desert. It is also useful as a fire retardant, an anti-fungal, and a bleaching agent.