painting over a painting?

I bought a frame from the thrift shop and the painting inside is crap.  I'm thinking of painting something in oils on top of the old painting

Advantages
- texture is all the rage so I'll get free texture
- I know it fits the frame
- panels in that size are crazy-expensive and hard to find.

disadvantages
- texture is annoying to paint on.
- the panel is a little bit warped
- there might be varnish and I'm not interested in working with the stuff needed to remove it.

What would I need to do to paint over an old painting?  Since I don't know if it's oils or acrylic, I can't use acrylic gesso in case it's oils.  Can I use oil based gesso?  Or just a layer of oil paint to "prime" the canvas.  

I don't feel that sanding is an option as I'm not doing well with dust this year.

The painting is old enough that "fat over lean" is unlikely to be an issue.  Fat over lean is a thing in oil painting when we paint in layers.  As oil paint cures, it expands and contracts.  So each layer needs to be more flexible than the last, and this is oversimplified to "fat over lean" meaning that each new layer has more oil (fat) than the previous ones.  However, if the paint has gone through the main curing phase (takes about a year for a thin amount of paint) then it becomes less important to worry about "Fat over lean" and just focus on the flexibility of the pigments (aka, limit burnt umber or other earth colours).

What do I look at?  What do I try first?
How do I paint over an old painting?  

If it's older, then a base coat of a suitable background oil colour should be enough. There is a very long history of oil being overpainted.

I've done painting on older canvas but that was altering the images rather than painting over the whole thing. I have done acrylic over an unknown surface and it was fine, but I only did that when it was on board. ( and I was pretty sure it wasn't oil)
If it was a cheap enough score, then it should be a fairly low risk gamble to try it.

Could you flip it over and paint on the back?

I often see paintings at the local flea market, some of them in frames, and always wonder about that. You might have to destroy the frame to do it though.

Vera Stewart wrote:Could you flip it over and paint on the back?

I often see paintings at the local flea market, some of them in frames, and always wonder about that. You might have to destroy the frame to do it though.

I had wondered that.

Sadly it's a canvas panel with canvas only on one side.

But it's a good idea.  With normal stretched canvas it's supposed to be easy to flip it and paint on the other side.

Dian Green wrote:If it's older, then a base coat of a suitable background oil colour should be enough. There is a very long history of oil being overpainted.

I've done painting on older canvas but that was altering the images rather than painting over the whole thing. I have done acrylic over an unknown surface and it was fine, but I only did that when it was on board. ( and I was pretty sure it wasn't oil)
If it was a cheap enough score, then it should be a fairly low risk gamble to try it.

That's good news.  I think I'll tone it with some palette grey (mixed up leftover paint from previous paintings) and let thag dry while I figure out what to paint on it.

So this is indeed a thing.  In fact a hidden masterpiece was found not long ago which was hidden underneath another painting, trying to remember which famous painter it was, I want to say Tissian?  (spelling??), anyways it was a huge surprise when it was discovered.

Towards the end of the video, she shows how to apply oil ground over old paintings.