Materials.

If you’d have seen the marble sculptures when they were new, you would have described them as anything but realistic. We now know that many, if not most, sculptures were painted in bright garish colours.

Why paint a delicately crafted sculpture with a dodgy paint job? Party taste, perhaps, but more definitely because that was what was available.

The paints that we have now are carefully designed, mixed and stored to deliver a wide range of colours of a consistent quality (and even modern companies like GW struggle with that!).

The further back you go, the fewer pigments there are and the less sophisticated the binders are. It’s no coincidence that the rapid explosion in science and trade of the Renaissance led to the rapid development of paints. Even in those days, an artist didn’t buy paint, they made it - access to new raw ingredients was all that was needed.

So, why the Renaissance? Because it’s the earliest point in time it could have been possible.