Knitters generally want to avoid the felting process after they've spent a lot of time knitting a project. But it is fun sometimes to throw all caution to the wind and knit a project to shrink it in the washing machine on purpose. The process of felting makes the material denser, wind proof, sometimes rain proof, and it shrinks the material. I could go into how the felting process works, but that can be googled.
First, choose the project you want to turn to felt. Sometimes you can find directions for knits specifically to become a felted project, but you can adapt. Next, you must choose a fiber which will felt. Animal fibers such as wool and angora rabbit will felt nicely. Mohair may or may not felt and it takes a lot to get it to do so. It isn't a good choice.
Here's the beginning step. Nevah, evah, skip this step because you need to know how much the fiber will felt and shrink and the only way to do this is to knit a swatch and felt it. Choose needles that gives the recommended gauge. Cast on enough stitches to make a swatch 5" wide. Begin knitting. There is no point in getting fancy because the felting process will hide the stitches. I use stockinette stitch. I aim for a not too loose fabric nor a tightly knit one, correct as to the gauge the pattern calls for. Knit until you get the swatch 5" long as well, bind off. We want the swatch a known width and length.
Now the fun part. If it will be a small project, you can felt by hand with hot water, clothes soap, and lots of abuse. Really agitate, twist, rub together, and pound the swatch. All the things you never would do if you washing a wool sweater. Keep this up for at least 10 minutes. The piece should have started to felt. Continue with the hot water and abuse until it has shrunk quite a bit. Rinse with hot water. Then continue, without soap to abuse the swatch. Keep track of how long you do this. When the felt is to the thickness you want (don't worry about how small or large it is at this point), rinse it with cold water, wring out the water and lay flat to dry on a bath towel.
The other way to do this is to throw the swatch in a washing machine with detergent and hot water. Note how long you let the wash cycle go so you can repeat it with the project. Then throw the swatch, which should have felted some, into the dryer. I usually do both the washing and drying with a load of clothes so that there is maximum friction and rubbing. After the dryer, lay it out flat and smooth it out.
Now it needs to be measured. The example I used was 5" x 5" but as long as you noted the measurements, it could be any size. Measure the felted swatch. OK, don't panic, we have to do some math. Ah, ah, come back here. It's not that difficult. We are looking for the percentage that it shrunk. Let's say we measure the felted piece to be 4.5" x 4", sometimes it doesn't felt evenly and there is a difference. 5x5=25 sq. inches. 4.5.x4=18 square inches. To get the percentage, take the smaller number and divide by the larger number to get a decimal. 18 divided by 25 = .72 multiply that by 100 and you have 72%. But, that's the amount of felt present. We need to find the amount it shrank. 100% is what we started with so 100-72= 28%. So, the swatch shrank by 28%. This is important information because it will tell us what number to use to figure the next bit.
We know the piece shrank 28%. If we were to cast on the recommended number of stitches and processed it to make felt, it would be 28% too small. This could be done if you knew you wanted to make something that much smaller, say for a child whose size is that percentage smaller than the original pattern. To make the felt the correct size, one needs to cast on 28% more stitches. All parts of the pattern need to be increased by 28%. So if the pattern says to cast on 80 stitches, we need to add 22.4 more stitches. That would be 80 x .28 = 22.4 You can't make a .4 stitch, so either add one stitch or ignore the .4. All the measurements of the project need to have 28% added to it because that it is what will be lost during the felting process. Length and width as well need to be adjusted upwards that 28%. Just follow the example I've given for finding and the percentage and calculating the end result.
Finally, process the finished garment in the same way as you did the swatch to replicate the reduction in size. It should turn out as the correct sized felted garment.
Lastly, you can needle felt appliqued type designs on the felted garment to decorate it.
Have fun!
