Oil Mediums & Varnishes
Traditional damar resin painting mediums were transported in socks. Yes - the Indonesian Makers would collect the dripping, oozing resins from the slashed trees in socks so the European Paint Merchants would buy by the "sock".
Most of that colorful trade has been replaced by synthetic alkyd resins and galkyd in Gamblin's version, a well respected product. Traditional damar mediums and modern alkyd serve to make oil paint more transparent and glossy. It also speeds drying. Alkyd medium has the advantage of not darkening with age but that Rembrandt darkness is lost with moderness.