Size is the gelatinous medium on which marbling designs are created, a thickened water base onto which the marbler drops paints. The surface tension of this viscous fluid causes the paints to take on a life of their own, spreading and interacting with each other in marvelous ways. When all the colors have been applied to the size, the marbler coaxes them into a pleasing design, then transfers that onto paper or fabric.
Size matters enormously. Its condition is crucial to the outcome of the design. Successful prints depend on healthy size.
Size that's too thin lets the colors spread too far and too fast. Size that's too thick doesn't allow them to spread enough. Dust on the size causes prints flecked with unattractive blank spots. Size contaminated with too much alum makes the paint clump into angular clots instead of spreading smoothly.
And perhaps saddest of all is tired size, size that has lost its spring, its will to support and spread color. Tired size drains the life out of paints, which lie lumpy and listless where they fall, refusing to blossom into the organic shapes that are the beginning of any marbling design.
How sad it is when this scenario signals the end of a marbling session! Like a carousel slowing to a halt with its music running down, the exhilarating ride is over and it's time to step off. All that remains is the clean up.
So, yes, as any marbler knows, size matters.