Method of making glass

A method of making a glass, the method comprising the steps of:

• (1) determining a final set-value concentration of a refractive index control substance depending on a target refractive index of the glass;
• (2) putting a soot glass deposit body having an effective portion in a container;
• (3) doping the refractive index control substance into the soot glass deposit body by supplying a doping gas into the container and discharging the gas from the container,
• wherein the doping gas contains the refractive index control substance;
• and
• (4) consolidating the soot glass deposit body by heating,
• wherein in the process of doping the refractive index control substance, the container is first supplied with the doping gas including the refractive index control substance having a concentration set to be higher than the final set-value concentration, then supplied with the doping gas including the refractive index control substance having a set-value concentration lower than the final set-value concentration or the gas including none of the refractive index control substance and finally, supplied with the doping gas including the refractive index control substance having the final set-value concentration into the container such that the refractive index control substance is doped into the soot glass deposit body, and
• wherein the refractive index control substance gas is flowed at a flow rate f satisfying an equation:
• f/V <0.012(minute−1), in which f (slm) represents a flow rate of the refractive index control substance gas and V (liter) represents a volume obtained by subtracting the volume of the effective portion of the soot glass deposit body from a capacity of the container corresponding to a part surrounding the effective portion of the soot glass deposit body.