I was given an oil based painting drawn by my relative (very dear to me). I live near the beach and we've had trouble with moisture/dampness. The painting is framed but not covered by glass or anything. Would it get affected/damaged by the salty air?
Oil paintings can be damaged by salt air and humidity. Other concerns are exposure to natural light, and sharp changes in temperature that can cause the paint to expand and contract and potentially crack or chip.
Rare and valuable paintings are kept under controlled temperature and humidity conditions and protected from natural UV light.
Two things that you can do to protect your painting are to keep it out of direct sunlight, and frame it with glass. There are two things to take into account if you protect your painting with glass, (1) the paint must be completely dry, and (2) the pane of glass should not touch the painting.
Please see a similar Stack question with mention of glass placement over an oil painting: Will putting an oil painting under glass cause damage?
It really depends on a lot of factors, not only salty air.
Does the temperature change drastically day to night? How is the humidity level, very high? Very low? Changing a lot day to night? Does the painting hang in a sunny (i.e. direct sunlight) place or a shaded location?
But yes, salty air will directy affect the oil paint itself (either by drying on the surface and leaving salty residue, salt is hygroscopic and will dry the paint out and probably lead to cracks in the paint) and the canvas. Depending on the type of frame used to stretch the canvas, it might be necessary to regularly check the tension, too. But especially a good treatment of the backside of the canvas will help a lot (e.g. sealing).
Problem is that usually walls are colder than the air in the room. This means that the painting which hangs on your wall is in the coldest area of the room (micro condensation can occur, leading to accelerated forming of cracks called "Craquelure" etc).
For an expensive painting it would be best to:
- get a proper frame (ask a specialist), UV filtering glass helps a lot (against UV B at least, UV A does still reach the painting)
- a proper frame will be well sealed not allowing a flow of air (which will transport humidity, dust etc.)
- try to make sure the painting gets max. around 150LUX of light
- a temperature of 18 - 20° C would be best
- humidity levels of 55-60% are optimal
If the painting is not very expensive but important to you, I suggest to put it somewhere without direct sunlight and if possible not on an outside wall. Simply use a dry and lint-free cloth to carefully remove residues (salt or dust) from the surface of the painting.