Don't let the intricacy and kaleidoscopic beauty of a marbleized design fool you. Those ripples of color may look hand-painted or machine-stamped, but they're actually created by liquid.
Marbleizing, which involves using absorbent papers to pick up ink from a water bath, dates to the twelfth century, when it was practiced in Japan and possibly China. Today, you can make your own rich designs by marbleizing paper to use as stationery and cards.
Marbleizing supplies are inexpensive and readily available at art-supply and crafts stores. You can easily make your own rake (for making patterns in your paint) by sandwiching toothpicks taped at 1/4- to 1-inch intervals between layers of corrugated cardboard.
Prepare the surface of your paper: Dissolve 2 tablespoons of the alum in 2 cups of warm water. Use a pencil to mark one side of the paper, then brush that side with the alum mixture. (The pencil markings will indicate which side you prepared, as the solution will dry clear.) Hang on a clothesline (about 1 hour) to dry; when dry, iron sheets on a medium setting to flatten.
In a bowl, combine 1/2 cup of methyl cellulose with 4 quarts cold water, whisking to incorporate powder. When the mixture is free of lumps, let it sit about an hour, stirring at 15-minute intervals until it is syrupy. Pour the liquid into an empty pan. Thin paints, until runny, with small amounts of water. Dip a brush into your first paint color, and hold it over the tray; tap on the handle with a pencil, letting the paint speckle the mixture. Continue to add paint (use up to five colors), covering as much of the mixture's surface as you like. Leave the speckles as they are, or speckle paint on solution to create a "stone" pattern.
Hold the paper by two corners and lower it (prepared side down) so it floats on top of the solution. Let go of the corners, and smooth out any air bubbles with your fingertips. (Air bubbles are inevitable, so don't fret if a few remain.) Let the paper float for a few seconds, then gently lift it from the solution.
Immediately after removing the paper, place it in a pan, and pour water over it. Hang paper to dry, marbleized side up. Do not touch the paper until it is dry (typically within 2 hours, depending on humidity levels).
Decide whether to keep or discard your solution (it can be used several times). To change paint colors, lay strips of newsprint across the solution's surface, then remove; repeat with clean strips until the solution is clear. You can store the solution in an airtight jar for about a week. Don't leave it in the tray, which could rust. If you have excess solution, do not pour it down the sink -- it may clog your drain. Instead, pour the liquid into a resealable bag or plastic container, and throw it away. (There are no dangerous toxins to be concerned about.)