The physical characteristics of a mantle depend upon the fabric and upon the rare-earths used.  It must not shrink unduly when burned, and the ash should remain porous.  It has been found that a mantle in which thoria is used alone is a poor light-source, but that when a small amount of ceria is added the mantle glows brilliantly.  By experiment it was determined that the best proportions for the rare-earth content are one part of ceria and ninety-nine parts of thoria.  Greater or less proportions of ceria decreased the light-output.  The actual percentage of these oxides in the ash of the mantle is about 10 per cent., making the content of ceria about one part in one thousand.

Mantles are made by knitting cylinders of cotton or of other fiber and soaking these in a solution of the nitrates of cerium and thorium.  One end of the cylinder is then sewed together with asbestos thread, which also provides the loop for supporting the mantle over the burner.  After the mantle has dried in proper form, it is burned; the organic matter disappears and the nitrates are converted into oxides.  After this “burning off” has been accomplished and any residual blackening is removed, the mantle is dipped into collodion, which strengthens it for shipping and handling.  The collodion is a solution of gun-cotton in alcohol and ether to which an oil such as castor-oil has been added to prevent excessive shrinkage on drying.

The materials and structure of the fabric of mantles have been subjected to much study.  Cotton was first used; then ramie fibers were introduced.  The ramie mantle was found to possess a greater life than the cotton mantle.  Later the mantles were mercerized by immersion in ammonia-water and this process yielded a stronger material.  The latest development is the use of an artificial silk as the base fabric, which results in a mantle superior to previous mantles in strength, flexibility, permanence of form, and permanence of luminous property.  This artificial silk mantle will permit of handling even after it has been in use for several hundred hours.  This great advance appears to be due to the fact that after the artificial-silk fibers have been burned off, the fibers are solid and continuous instead of porous as in previous mantles.

The color-value of the light from mantles may be varied considerably by altering the proportions of the rare-earths.  The yellowness of the light has been traced to ceria, so by varying the proportions of ceria, the color of the light may be influenced.

The inverted mantle introduced greater possibilities into gas-lighting.  The light could be directed downward with ease and many units such as inverted bowls were developed.  In fact, the lighting-fixtures and the lighting-effects obtainable kept pace with those of electric lighting, notwithstanding the greater difficulties encountered by the designer of gas-lighting fixtures.  Many problems were encountered in designing an inverted burner operating on the Bunsen principle, but they were finally satisfactorily solved.  In recent years a great deal of study has been given to the efficiency of gas-burners, with the result that a high level of development has been reached.