At that time I had no sphagnum moss so, instead of using the conventional substrate, I used peat instead (peat is just broken down sphagnum moss anyway so I thought it wouldn't do any harm). I used an old kitchen knife -which was sterilized in a pot of boiling water to prevent fungal infections from harming the new roots- and made a ring (around 9cm thick for a 6cm trunk) and cut my way through the bark until reaching the sap layer -a hard light woody section) where I scraped away the thin layer of cambium to reveal a lighter white wood underneath. The ring was constantly the same thickness all the way around the trunk and made sure there were no bridges where the tree could heal the wound instead of produce roots.
I then placed a sandwich bag with an opening at both ends around the trunk and tied it in securely just below the incision. Filled the back up with my soaking peat until I couldn't see any signs of the cut -make sure you really pack your substrate in so there are no air bubbles- and tied it in at the top with another wire tourniquet. After securing it at both ends with a second piece of wire I wrapped the ball of peat and polythene in cling film until I could just about see the substrate. The cling film wrapping has a tendency to become highly addictive and caused me to go a bit over the top at one point.
Well, after many months of anticipation the time came in which I could unravel the polythene from my air layers. After checking there was sufficient roots under both layers I severed the bottom using a saw. After this I carefully removed the polythene from my air layers to discover a mass of plump, white roots. A good technique I've learnt to remove the soil/moss from the roots with minimum damage is to dunk the roots into a bucket of water. Sadly I forgot to take a picture of Pyracantha Air Layer [1], but here's [2].
As you can see from photo I cut a bit too far down, that can be solved next re-pot (at least it's better than cutting too high). I will update with new pictures of each layer as they develop if they're interesting enough to show.