You have to do this outside as this is very stinky and you don't want to breathe in a lot of these fumes, so take precautions please. Wear rubber gloves for this project.
First you have to find old National Geographic mags that are 2004 or older because the pages are clay coated and that's what you need for the technique to work. I found mine at a thrift store for 39 cents a piece. I found out that all the pages in the magazine will not turn. Most will, but not all.
You need turpentine and a sponge brush and a container to keep your magazine in while it is soaking. Also you will need freezer paper or something to put the pages on to dry.
Take the book and tear the covers off. Discard them. Take out any paper cardboard pages. Tear the book into several sections making it easier to handle. With the brush start covering each page of the book with turpentine.
I covered all the pages in the whole book and let them sit stacked up on each other in the container for 3 hours or so. Then after I knew the process had taken place, I separated the pages one by one. Do not let them dry out during that 3 hours before the turpentine has time to "melt"the ink on the pages, as this will stop the process. As the process is taking place you can smush the pages around to intermingle the colors.
When you separate the pages lay them on freezer paper to dry, which should not take long. The smell will last for awhile I have read. Then when you use them for your journals and cover the pages with sealer or paints or gesso or whatever then the smell will not be there anymore. I have read that you can also buy a product called Cytrasolv or an odorless turpentine, which I have not found either one.
I love the way the pages came out and I will be using them in journals. The paper is strong and does not get weak and tear when it is wet with the turpentine so be sure and soak it well when you are doing this. I hope you try this as it is very unique and you never know how your pages will turn out. When you peel the pages apart it makes unique marks on them. Depending on what is on the page originally will determine the outcome, so colorful pages make the best turp pages I think.