You start with whatever it is you want to put a crackle finish on. It works on just about any surface. I've crackled both wood and metal. Today I'm crackling a wooden frame I got at a thrift store for $3. It's actually a nice frame but all the other frames on my wall are light colored and this one just overpowers the whole wall.
I taped off the areas I didn't want to get paint on. Whatever color your item is now is the color that will show through the crackles. So if you want the base color to be different, paint it now. I thought the golden brown color of the frame would look fine showing through the crackles. Actually, I was just too lazy to paint it.
Now you slap on a fairly thick layer of plain ol' Elmer's glue. I buy it by the gallon at WalMart because I use it for a lot of different thing. Sometimes I even use it as glue.
I found instructions for this technique on several different websites and they were all a little different. One site said a thin layer of glue won't crackle, another said a thin layer of glue will give you finer crackles. I avoided this controversy all together by just using a thick layer of glue.
You're supposed to let the glue set just until it's tacky. Don't let it dry all the way or it won't crackle. Personally, I wasn't aware that Elmer's ever got tacky. In my experience it goes from extremely wet to extremely wet but with a skin on top. Then 4 days later it's dry and whatever you put it on is buckled beyond all repair. That's the joy of Elmer's.
One website said it should be tacky in about 5 minutes. Another said it should be tacky in just over one hour but under two hours. Normally I would average two conflicting suggestions but that's a big dang gap. So here's what I did. I brushed on a thick layer of glue then played Zuma Blitz while waiting for it to tack up. I got my best score EVER in Zuma so naturally I got all absorbed and played a bunch more games and forgot all about my wet glue. By the time I remembered it was mostly dry. You could call that a mistake but I prefer to call it research. Each game of Zuma lasts one minute and I only have 9 lives so I probably wasn't playing for more than about 15 minutes. That bit of valuable research told me that the one hour drying time must be for people who live under water and I should use the 5 minute drying time suggestion. See? Research.
I slapped on another layer of glue then tried not to wander too far away from the table or else I'd forget about it again. I used the leftover glue that I left sitting out in a bowl so it had thickened up and started drying faster. I liked that and decided to make sure I leave the glue out for a while before using it since it not only dries faster but it sticks better since it's not so runny. I really hate Elmer's glue, I just have to say that.
For the record, I don't think it ever got what I would call tacky. In fact it was still pretty wet when I brushed the paint over it. I think the key is just to make sure that you're able to paint over it without mixing the paint with the wet glue. Letting the glue thicken helped with that a lot. Also, you want to load your brush with lots of paint so that you can cover an area with one stroke. If you go back over it or use back and forth strokes, you are more likely to get some glue mixed in with your paint and then your crackle is screwed.
I did the four sides of my frame one at a time which worked just fine. If you try to do too large of an area you run the risk of your glue drying before you get the paint on it. After painting one section I moved to the next section and brushed on the glue. By the time I was ready to paint the second section, the first had already started to crackle.
Here is the finished frame which blends nicely with the rest of the frames on the wall. Well, except for the couple that I haven't painted yet. I can't say exactly how long it took the whole thing to dry but it took a while. I set it outside in the sun (100 degree sun) for a couple of hours which worked great.
I have a theory about how this works. I don't know for sure and it's not like it matters but it fascinates me so I have to try to figure it out. I think that Elmer's glue buckles paper so badly partly because it's such a wet glue and partly because it seems to shrink as it dries. Shrink is probably not the right word. It draws up. Paint doesn't shrink when it dries and the paint dries a heck of a lot faster than the glue. So basically the wet glue draws up under the dry paint causing it to crack. I think it's plausible.