Can I use Mod Podge to seal my oil painting?

M Winther said:

It is not necessary to varnish an oil painting in today's clean aereal environment. I don't know why people keep doing it. Braque never varnished his paintings. Of course, one reason could be to even out areas with different shine.

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You're correct it's not necessary to varnish an oil painting. But, most of the time the painting dries matte in some places and glossy in others. Adding a varnish at the end will even the whole thing out and bring the color back. I use gamvar varnish after my painting has dried for months and it's like Christmas every time. The painting looks brand new again.