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Thankyou very much for all your suggestions, I have managed to grasp the concept though and I can now get my head around the equasions. A very interesting suggestion though that opaque materials may be transparent if you broke them down further.

so if this energy difference does not correpond to the energy of the photon then light will pass straight through? what about white paper? Is this because in white paper the photons are absorbed but simply re-emitted imediately, unlike in water where they are not absorbed? thankyou very much by the way alien.

I hope this is not considered spam as I have posted this elsewhere on the forum but wasn't sure of the right place for it. sorry if it is. To the best of my understanding materials are opaque when the energy of the photons are absorbed by the electrons raising them to the next energy level within the atom/molecule. This energy is then given off as vibrations, heat or as another photon. please correct me if I am wrong thus far. I do not know why this occurs in some materials and not others, I think it's because in opaque materials the wavelength of the electrons match those of the photons in coloured materials and in black materials all the wavelengths of visable light are matched. however this makes no sense to me as surely white materials (not absorbing any but reflecting it) and transparant materials would be the same. so what makes some materials reflect light and some let it through unaffected (or slightly refracted)?