I've shrunk two of the Desiree molds (Fashionista and I Can Be) and both reduced to the exact measurement each time.
I used thread to secure the hair from floating around as I thought a rubber band might turn to mush and get stuck in her hair. Then I poured the bottle of remover into a clean pickle jar. Using tongs, place the head into the jar, making sure to hold it until the neck hole fills with liquid which makes the head stay down and not float. Cap the jar and let sit at least 36 hours.
I do not rinse the head with water when I pull it out. I just pat it dry, being very careful not to touch the face paint. I try to time it so that I sit the head outside for at least 5-8 daylight hours, but not in direct sunlight! I've never done this during cold weather so I don't know what effect that might have.
Once I bring it inside (sometimes I leave it out all night), I wash the hair and put conditioner in it for about 15 minutes. I still don't rinse off the face though. You could probably skip this step but I have a problem with the odor so I want it gone soon as possible. After 8 hours it's reduced as much as it's going to for this first time. If you want to try to make it smaller, dip it again for another 36 hours, but I would do it in a fresh solution. Double dipping or using the same solution for multiple heads doesn't seem to work.
I've had success with multiple dunkings of a LIV head. The circumference of the original head was 5.50". The first dip reduced it to 5.38" and the second to 5.18". However, there is only so much give in the vinyl. I don't think you can make a LIV head Barbie sized ('least I haven't tried it). One dip of my Monster head reduced it from 5.28" to 5.00". I didn't dip it again because I liked the proportions it had on the Fashionista body.
You have about 48 hours from when you start the drying process before the head begins to harden. Once it's completely hard (after 4 days tops), that's it. You can't shrink it again, reroot it, reinsert eyes or remove it from the body you've placed it on.
Things I learned the hard way:
- Don't put the head on the body until it has dried for at least 8 hours. If you put it on before it has enough drying time, it will eat the top of the neck hole and make it mushy.
- Take the eyes out of a LIV head before reducing or they will melt into goo!
- Use fine sandpaper to contour a face after it hardens, not your Dremel. Otherwise, you'll get groves instead of a smooth finish (see photo above).
- Don't bother with the Target brand remover. It's not effective at all. I have found that I prefer to use Walgreens "Studio35" brand. It's the purple colored one and comes in 8 and 10 ounces.
Check out this Dec 2012 post, "Fun and Failure with Acetone" for more info on shrinking doll heads.