As one binds (softens) gold by means of lavana (borax), and silver by means of gold, and tin by means of silver, and lead by means of tin, and iron (loha) by means of lead, and wood by means of iron, or also by means of leather,

In plain words: People join metals using other materials. Gold is joined with borax, silver with gold, tin with silver, lead with tin, iron with lead, and wood with iron or leather.