These are marketed as student grades. Archival quality watercolor papers have a neutral PH value. The surfaces are very durable, but you must alter your technical approach due to their unique absorbsion and working properties. Papers are sized with gelatine. The amount of sizing determines the amount of color the paper takes into its structure.
Heavier sizing allows more color to stay on the surface and allows easier reworking of the paint.
Internally sized paper has the sizing added in the vat before the paper is made. Tub sized papers are soaked in a sizing bath after the paper is made Tub sized paper is the preferred choice of watercolorists. The weight of a paper is determined by the weight in pounds per square meter. Traditional paper for watercolor range from 70 lbs. When dry the surface can be worked without warping due to water absorbsion.