Some thoughts on where to get the paper for paper clay

What is a good source of paper to use for paper clay? I use cellulose insulation in the clay. I purchase it a Lowes and it comes in 30 lb bags. There are two advantages to this source. (1) You don't have to make the paper fibers. (2) It preserves the paper clay. As you know, after you keep paper clay for a few weeks it starts to rot and turn black. Cellulose insulation had borax in it and as a soluble salt, it makes it much harder for the rot to occur. This borax does cause a slight problem in the clay. Borax is a strong flux and will cause the clay to mature at a lower temperature. I get around this problem by using a higher firing clay and fire to a lower temperature. This works great. I use Standard 257, cone 10 porcelain and fire it to cone 6.
If you want to make your own paper fibers I would use newspaper. Mix the paper in a large bucket of water and let it set for about an hour. I use a drill with a mixer attachment (large works best) and let it run for about ten minutes. You can test the paper fibers to see if they are ready by dipping a small amount into a glass of water. If the fibers are ready the paper will disappear in the water. I put 800 grams of paper in 50 lbs of clay. This about a five gallon bucket full. As I said, 50 lbs of clay, 1 gal of hot water, and 800 grams of dry paper fiber. You can add a lot more paper to the mixture. During the recent international paper clay conference in Hungary, I use the lowest amount of paper compared to the other artists there. If you were going to make sculptural forms you could go as high as 50% (by weight) of paper to clay. This is a lot of paper!
When I give my workshops, I have a test piece of pottery where the mixture was 90% paper and 10% of clay by weight. I pressed this mixture into a mold and fired the piece. It worked! It was like a chunk of coral. Funny stuff paper clay.
An additional tip.... If you mix sources of paper. Beat the different papers by themselves in the bucket with water. Then combine the desired mixture. If you mix papers you will over process some of the paper and under process the other.
Tip #2.. To preserve paper after I have mixed to get the fibers broken dow, I freeze them in the refrigerator. This preserves them for a long time until I need them. I just add them to the bucket with the hot water.