Complex sentence: Differential tempering is obtained by quenching the sword uniformly, then tempering one part of it, such as the spine or the center portion of double edged blades, with a torch or some other directed heat source.
Split into simpler sentences: Differential tempering is obtained by quenching the sword uniformly, then tempering one part of it, such as the spine or the center portion of double edged blades. This is usually done with a torch or some other directed heat source.