Luckily for us, improved methods have developed since. While one can make natural starches from potatoes, rice, or gelatin, it is more common and easier to simply purchase chemical sizing from papermaking suppliers. Both methods have their benefits, and some papermakers even use a combination of both techniques. Internal sizing is an easy way to apply a coating to individual fibers, but still allow for some absorption of oil or water based ink or dye. All the paper made from one batch of pulp is equally sized.
External sizing is more time consuming, but has some advantages.
Individual sheets can be sized differently, for instance, if destined for different uses. Surface sizes do not envelop individual fibers but add a protective coating to the sheet itself, inhibiting any absorption or bleeding. While this is a helpful quality for calligraphers, some do not care for the appearance of handmade sheets with too much surface sizing. Use a large soft brush for quick application, or a simple plant sprayer if the size is fairly thin so as not to clog the sprayer. Or, run dry sheets through a tray of sizing liquid, or soak them in the tray for several minutes followed by a light pressing.