Abstract: In a method for making optical fiber preforms, the time taken for sintering and annealing the clad or jacket layer is significantly reduced by only partially sintering the jacket soot boule in an atmosphere of helium. For example, instead of using one hundred forty-three minutes to sinter completely the soot boule, the boule is only partially sintered by heating in a helium atmosphere for fifty-nine minutes. At this stage of course, the soot boule is still partially porous and is generally opaque. The completion of the sintering and the annealing is then done in a single step in an atmosphere of nitrogen. Surprisingly, we have found that this process does not entrap nitrogen in the soot jacket layer to any noticeable or harmful extent, and the total time for sintering and annealing is significantly reduced.