Conditioning is desirable principally on account of the fact that raw silk absorbs considerable moisture. A careless buyer may find after delivery that he has purchased more water than he has silk. To avoid this possibility, Asiatic and European markets in particular have adopted the conditioned weight basis—absolute dry weight plus 11 per cent moisture. Quotations are often given on invoice weight, which is conditioned weight plus a 2% margin for variation. A conditioning house, besides examining for weight, also conducts numerous other tests necessary to conditioned silk. The main factors taken into consideration, besides weight, are size, color, cleanliness, boil-off, winding strength, elasticity, and general uniformity. [Sidenote: _Weight_] As regards size, the unit is the denier, an ancient French weight equal to .05 gram; the size is measured by the weight in deniers of 450 meters of the thread. As previously stated, the 13/15 denier size is the standard used in the United States, although the larger and smaller grades are dealt in to some extent for special types of products. Size is always given as averaging between certain deniers (such as 13 to 15) as it is impossible to attain absolute accuracy in reeling, and slight variations cannot be avoided, either within the bales or within the skeins themselves. [Sidenote: _Color_] The color test is concerned merely with uniformity in shade, which makes accurate dyeing possible. The cultivated silks are either pure white or yellow, according to the variety of cocoon from which they are derived. [Sidenote: “_Boil off_”] The term “boil off” refers to the amount or percentage of gum on the filament. As explained before, the individual strands of fibre adhere together through a gummy substance secreted by the worm. The amount found in the reeled silk varies with different kinds from 10 to 25 per cent by weight—which is brought down to a minimum by the boiling process. [Sidenote: _Winding Strength_] Winding strength is measured by the breaks that occur in winding. In this country the test is based on the number of breaks occurring in 30 or more skeins wound at the rate of about 120 yards per minute. This test is extremely important since a weak thread can do much to hinder an efficient re-reeling process, inasmuch as each break stops the machine and must be tied by the operator. 3. GRADING AND QUOTATIONS [Sidenote: _Classification_] [Sidenote: _Difficulties in Grading_]