A few weekends ago we got out the Kid Concoctions and Contraptions book again, and thoguht we'd try the crystal growing. It seemed pretty simple, and we had all of the things we needed. The first thing we did was find some shells and rocks to put in the bottom of a bowl ... I put the rocks we gathered from our backyard on the table, and Taipan noticed that we brought something else in too - a slug. He was tiny. We watched him slime around our table for a few minutes, and then decided that he'd be happier outside.
Next we mixed alum with hot water, and stirred it up for a long long time, waiting for the alum to dissolve (which it never completely did).
Then we poured the alum and water over the rocks and waited for crystals. In a few hours we thought small crystals were forming on the side of the bowl, but nothing other than that ever grew. We left the bowl out for about a week before emptying it.
The great thing about all of these experiments / projects we've tried from that book is that for the kids it's all about enjoying themselves, and the journey. They haven't ever cared whether or not we get the expected outcome. It took me a while to get to the same place :-) They love trying new things and spending time together ... I know they would have thought crystals were cool, but it didn't ruin their day (or their moment, or their memory of the experiment) when we didn't get any crystals.