Root Over Skull Plans

Getting everything straight in my head as to exactly how I'm going to do this is, IMO, key to succeeding at it.  My previous attempt at root over rock ended up having some very good looking results, but it did not grip the surface as well as I had wanted.

The method I used at that time was a pull down.  Basically it involved burying the object I wanted it to grow over and putting the plant directly on top of it.  Then every 2-3 weeks I pulled the soil level down about an inch.  This meant the pepper had to constantly grow it's roots deeper and deeper to stay in contact with the soil, while the exposed root lignified and thickened.  The result was pretty nice, as far as the roots themselves went.

You can see by the third picture however that I had it tied down to the base because while the roots looked very nice, the plant at that point was basically sitting on the ornament, it wasn't actually gripping it.  I had planned on going back and doing some scrapings to get back down to the cambien and re-burying it to encourage more roots to grow and grip the piece, but an unexpected late frost ended up killing this one out in my raised bed before I had the chance.

I've been doing some research on ways people have done root over rock for odd shapes, and hit on this blog that has what I think is a fantastic idea.  It essentially combines two of my interests into one project, making this bonchi, and making molds for things like masks and special effects makeup.  For those that didn't read the link yet, he basically covered what he wanted the bonsai to grow on in paper mache, then used spray foam insulation to make a mold over it.  Cleaned out his mold, arranged the roots how he liked, put some medium over them, then sealed the mold back up.  That made sure to keep a nice even pressure over the whole odd shape while creating an insulating layer that protected the tree from temperature changes.

I've seen other people do similar with plastic wrap, but had concerns about how well cling wrap would work with all of the odd shapes of a skull.  If I do it this way, I can ensure that the roots have nowhere to go but exactly where I want them.

I'll keep researching ways to do this, but I really like how this one appears to work, especially with how it will let me force the roots to curl up under things like the cheekbones and around the curve of the back of the skull.  If I can get all of that, the plant should be locked firmly in place.