One of the issues might be if you are modeling the head out of solid clay. It can add up pretty fast. Usually to keep things light people will build a wire armature or framework for the head. In order to fill up the volume of space that is the head so it can be coated with a layer of clay... aluminium foil is used to fill that space... crumpled into a ball or egg shape it remains light but can be packed very dense so it supports the clay as you model the facial features.

If you don't have any intention to bake your clay (depending on your final use and what clay you are using) you can use just about anything that is light but rigid. I've used small bits of egg shaped polystyrene from the craft store wrapped in wire so they clay has something to grip. There's any number of ways. I think aluminium foil is the easiest and cheapest for most people as it's readily available and cheap.

You can look at my simple walk cycle vid (under my profile) to see the polystyrene head on a wire armature body. Either type will sort out your head weight issues. Good luck and post up what you make so others can give you input.

Those are really nicely done. Character design is sussed. The frog head could easily be made out of aluminium foil on a wire armature. No problems there. You just have to dig in and give it a go. But it would only take you a few minutes longer than a regular armature.

At the moment he is made of solid clay?

Hi, I've taken your advice and started to make a head with a foil core.  Take a look at the attached, it's only work in progress, but it's much lighter.  Thanks again for the help.

Thanks Bagi80.  Much appreciated.  I need a lot more practice finishing things off, not bad up to the point where anything other than my hands or a scalpel are involved.  Are there any turorial decent videos around showing finshing techniques using tools etc?