One embodiment of the disclosure relates to a method of cleaning silica-based soot or an article made of silica-based soot, the method comprising the step of treating silica-based soot or the article made of silica-based soot with at least one of the following compounds: (i) a mixture of CO and Cl2 in a carrier gas such that the total concentration of CO and Cl2 in the mixture is greater than 10% (by volume, in carrier gas) and the ratio of CO:Cl2 is between 0.25 and 5; (ii) CCl4 in a carrier gas, such that concentration CCl4 is greater than 1% (by volume, in carrier gas). Preferably, the treatment by CCl4 is performed at temperatures between 600° C., and 850° C. Preferably, the treatment with the CO and Cl mixture is performed at temperatures between 900° C. and 1200° C. The carrier gas may be, for example, He, Ar, N2, or the combination thereof.