You can use exterior latex house paint that's been thinned. Billie

This is not my idea.I found it on the internet and it sounded interesting.

Bird bath make over

Spruce-up an old concrete birdbath by giving it a bath of color. Simply take a blue-green oil based paint (Sherwin Williams #2257 works the best) and thin it with 75% mineral spirits. Then brush the mixture onto the concrete surface. Once the paint dries and has fully soaked into the concrete simply smear the entire birdbath with vanilla yogurt. (SEE who said I can't cook!!) Now it will be ready for the final touchÂa good burial! That's right, just dig a hole and bury the birdbath for about 2 months. When you dig it up, the yogurt will have aged to a mossy green color and the thinned paint will be a perfect accent color for the new "ANTIQUE" birdbath.

LOL - I am laughing because that last posting was like reading a novel whose end could NOT be anticipated. Would LOVE to see the finished product if someone has ever done that!!! I researched that and have the link to the original source. Wish that person would have posted a photo.

Here is a link that might be useful: Buried Bird Bath source