There are many ‘household’ ways to clean an oil painting safely. To start with, generally, I would suggest taking the painting to a reputable art restorer. They are professionals that in the long run could save you money, time, and your painting. There may not be too many advertised in your local area but planning a visit to a city such as London may well be worth it.
Most major cities such as Paris, New York, and Sydney will have established and recommended art restorers such as Simon Gillespie in London. If you are unsure, you could speak with the artist you purchased the art or the gallery. Many auction houses will be happy to advise on local art restorers or galleries in your area. However, if it is just a bit of light cleaning, such as dust, this is easily cleaned at home with a clean paintbrush. Cotton wool buds will also gently lift off any dust.
It is worth noting that using water, alcohol, or any substances found in art shops should be treated with care. If you don’t know what you’re doing, you can easily take off a layer of paint and cause significant disruption to the color of the painting and its composition. Art restorers will take the time to analyze the dirt; it could be smoke, nicotine, or general dirt from being transported and the handling. If the painting has been neglected or stored incorrectly there are probably remnants of cobwebs and insects. The solution is usually found through examination and only professionals can determine what has caused the dirt or damage to the painting.
If it is a large painting hanging in a hallway or house using a feather duster will do the trick. If you do want to get into any creases and corners of the oil paint it is best to place the painting on a flat even surface and find some bread. Yes, bread can help remove dirt from the bits that a duster will not reach. The soft white part of a loaf can be torn up and gently maneuvered around into the dirty areas. The breadcrumbs can be brushed off with a small soft paintbrush. Although again this method is not recommended for every painting especially if it is old and cracked and needs a bit more attention. The bread could also stain and affect the original paint causing even more damage than a bit of dirt.
A clean cloth damp cloth could also be used but depending on the value of the painting I would not suggest cleaning large areas. Pure turpentine can also clean paintings bearing in mind that the turpentine can also remove the oil and discolor the painting. I use turpentine on linen areas that have become dirty but very carefully.
If the painting requires a bit more than gently dusting off and has obviously caught smoke residue causing discoloring it would need a varnish to take the dirt off. What sort of varnish would be needed would depend on the substance or kind of dirt that has caused the problem. Interfering with a layer of paint and then the ingrained dirt on top could damage the painting even more. It is time-consuming researching the right sort of cleaning substance and the cost of the products themselves could all be in vain if you are not sure what you are doing.
If cracks have appeared on the painting or there is flaking paint, it would not be recommended to start any cleaning processes at home as you are probably more likely to take off more of the flaky paint and begin to create a new layer of problems that will need addressing.
The reverse side of the painting can sometimes need cleaning using a soft brush to remove any residual dirt and bits from inside the corners of the frame. If the painting is wrapped in bubble wrap, the insects, etc., can still find a way to ‘get in,’ so it is worth cleaning these areas. A museum vacuum gently lifts out any dirt or cobwebs.
There are many other suggestions and ideas around cleaning oil paintings but I highly recommend gently cleaning with a feather duster and leaving the rest to an expert.