Marbling is a great weekend project. The process is fun and the results are beautiful!
The actual marbling can be done fairly quickly, but the preparation does take some time. Read through the instructions carefully before you start!
What you will need
- buckets/trays
- paint
- jars or containers
- paintbrushes
- skewers
- marbling size (carrageenan or methylcellulose)
- alum
- newspaper
- paper
- cardboard
- cloth pegs
Prepare the Paper
Choose paper that is a bit flexible to start, it is possible to use heavier weight paper, but more challenging. In order for the paint to adhere well to the paper, you must apply a mordant (a substance used to make the paint stick to the paper). The one most commonly used by marblers is aluminum sulfate (alum). Alum powder can be purchased at your local art supply store. Dissolve 1/8 cup alum in two cups of warm water. Once the alum is dissolved, you paint it on the paper. Usually, I apply alum to both sides of the paper otherwise I forget which side to use. As you know Alum is also used in pickling, and you may have some in your spice rack – this is not the same type of Alum (Pickling Alum= Aluminum, Potassium, Sulfate as opposed to mordant Alum=Aluminum Sulfate), however, I have tried it and it works as well.
After the alum is applied, hang the paper to dry. Once the paper is dry, press them under books to make them flat – it will make marbling much easier if the paper is flat. It is not possible to marble with the alum wet on the paper (the paint slides off). 
Prepare the Marbling Size
Marbling size is the thickened liquid that the paint floats on. You will need to prepare the size a day in advance so that it is set properly. I prefer to use carrageenan for my size, but you can also use methylcellulose. Carrageenan and methylcellulose can be sourced at your local art store. Before you go to look for it call the store to see if they carry it (and save yourself a trip) – in Vancouver the only place I have found that carries them is Opus art supplies. Dissolve 2 tablespoons of carrageenan in 2 cups of water – you must stir it vigorously (I use both a whisk and wooden spoon), and then add enough water to make 1 gallon (16 cups) while stirring. The carrageenan must sit for at least 12 hours to set properly and then you can pour it into the marbling tray. The cheaper alternatives for making size is methylcellulose. You need to mix the methylcellulose with ammonia to create the marbling size. I find methylcellulose a bit smelly, even after the marbled paper has dried, it smells.
Prepare the Paint
The key to the paint is that it must be thin enough. I have used both acrylic and water-colour paint, and both work well. You can start with any paint (except oil) you have around the house and add water until it is thin enough to pour like juice. Some marblers use ox gall or a synthetic equivalent to thin paint, but I have mostly used just water.
Making Your Tools
Find some good paintbrushes – although one is enough if you clean it between using different colours. I have used all different kinds of paintbrushes but I prefer the calligraphy paintbrushes, they carry and drop the paint well. You can also use an eye dropper to drop the paint on the size if you want to be precise with colour. Once the paint is on the size, you need tools to create designs. I use skewers and homemade rakes. The easiest rake is made with cardboard and skewers (see photo). You can also make wooden rakes with a drill and some nails. It is good to have a variety of sizes of rakes – it will make the patterns more interesting.
Now for Marbling!
You are now ready to marble. Pour the marbling size you have made into the cookie tray or shallow rectangular bucket and you are ready to start. Use the paintbrush to drop your first colour of paint onto the marbling size, then add the other colours (do not touch the surface of the size with the paintbrush, let the paint droplets fall onto it). There is no rule about how many colours you can use, just experiment. Use the skewers to create patterns in the size. If you are happy with the design you created, carefully put the paper down on the size and the paint will instantly adhere to the paper. I usually pull the paper over the edge of the cookie tray to press out excess carrageenan. Once you have pulled the paper off the tray you can hang it up to dry. Use newspaper to skim the surface of the size (cleaning it) before you make another marbled paper.