I would have to agree with Mark on this topic. I think he made a very good point with:
By it very nature, bonsai is unnatural
There are only varying degrees of cosmetics/trickery/props etc. They range from crass and ineffective (laquered leaves) to the subtle and transparent (well Dremeled jins and glued on quince fruit on quince trees). The fact that bonsai is unnatural is a given. The proof of an "award winner" is if it's "unnaturally natural" and moves the viewer.
I didn't really look at it this way until he mentioned it, but the truth of the matter is, you can't allow one cosmetic enhancement and then say that another is out of line. Can you? I'm relatively new to bonsai, but it seems to me that one of the main focuses in this art is to create a tree that is styled by human hands, yet looks like human hands have never touched it. So, why exactly does wiring branches, carving deadwood and jin, and techniques like Thread and Pheonix grafting have credibility over covering missing bark or dying leaves?
I guess it really all boils down to how you look at bonsai. If you look at it from a perspective that it's strictly horticultural, then of course using clay to thicken the trunk of your bonsai or waxing or dying leaves would be out of the question, because the focus of your tree would be the horticultural skill used in creating it. However you would also have to rule out grafting and carving, since those are blatent handmade aesthetics that have nothing to do with horticulture.
But if you look at bonsai strictly as art, then anything goes really. And that could be dangerous in the sense that the exreme of that is a plaster of paris mold that is expertly crafted and painted to look like real bark, and then real leaves are glued onto it.
The reason that we find guidlines so difficult to pin down in bonsai is because it is neither strictly horticultural or art. It's both. So there is some blurring.
I would ask Will Heath why certain techniques he considering "cheating"? The most obvious reason that I find some of these things intially "wrong" is that it seems to take away the main driving force behind a powerful bonsai, and that is the patience of it's owner. If I see a bonsai with really gnarly trunk, lots of character and thickness and taper, then I'm impressed and the tree can move me. If however, I later find out that most of the character was actually chunks of clay molded to look like a rotted out branch, then I suddenly lose most of my respect for the tree as a bonsai (even if it may be a good work of art) mainly because the illusion of age has been shattered. I now *know* that the look of the tree was achieved in the amount of time that it took the artist to sculpt the features and fire the clay.
To me, there's a sense of awe that comes along with looking a tree that has taken decades to get to where it's at. I admire, more than the horticultural or artistic side of bonsai, the patience. And if whatever you are doing seems to have the sole intention of "speeding up the process", then that ruins it for me.
But I would like to hear many reasons why I'm wrong as well as other reasons why some of you may find some of these things "improper" in the world of bonsai.