A friend of mine owns a few paintings by Maxfield Parrish - but not 'Daybreak', above.
He was, as far as I know, the last painter to use the 'glazing' method and egg tempera together, producing wonderfully vibrant and luminous images like the one above. It's a shame that they were mostly chocolate-box illustrations, but they were not all like that. Some were dark and brooding, with the light seemingly coming from the painting itself - soft but intense.
The reason why these paintings seem to exude light, is because the ground for them is pure white, and the paint is applied in layers of pure colour (starting with the blues and ending with the reds) and between each colour layer, a coating of clear varnish is applied. This means that the natural light travels through all the layers, hits the white ground behind, then reflects back, so the entire painting behaves in much the same way as a stained-glass window does. It is also a similar technology to the offset-printing method, but there is a wider choice of primary colours. It can take months or years to complete a painting like this, and M. P. usually had about 10 on the go at any given time.
You know those Old Masters, which - although they seem to be almost a dark brown or black - seem to glow in ordinary light? Well, they were glazed egg tempera, which is why it is so utterly stupid to try to 'clean' them, as a lot of galleries attempt.
All the Egyptian tomb-paintings are either encaustic (beeswax medium), or egg tempera - it will last forever in the right conditions.
When I look at 'Daybreak', the taste of Restsina wine and the memories of a couple of American girlfriends come flooding back to me.