A varnished painting has a strong layer over the paint and this allows the painting easy handling over a matter of cleanliness.
Varnishing makes paintings easier to clean with not much of a hassle.
If a painting is not varnished, most often it would be damaged or spoiled.
When a painting is done, the oil paint dries out leaving a matte finish result.
In order to varnish an oil painting, you need to wait till the drawing is completely dry.
This in effect will take a longer time before a painting can be presented.
First thing you need to do is to clean the painting first.
You may use a liquid detergent of some sort to clean the painting.
Mix the liquid with a reasonable amount of cold water to clean the whole painting.
Then take any piece of cloth and dab it in the liquid water mixture, rubbing gently on the unvarnished painting.
Repeat the same action with clean water so as to not leave unwanted liquid stain that was used earlier.
After that, leave the painting to dry in a place that is reasonably warm.
In my opinion, find a place that is warm and dry with good temperature to proceed with the varnishing process.
This is because a moist environment would seemingly allow the varnish to appear in white patches and this is not wanted by any painter at all.
There are varnishes that come in spray bottles and they dry up real quick, although most artists still prefer to varnish their paintings with their own brush.
If you prefer to apply with a brush, choose a wide and soft brush for easy application.
Now, let the painting lie flat on a surface.
Then pour some varnish into an empty case and gently dab the brush with the varnish and onto the painting.
When applying the varnish, never brush up and down as this will only make the varnish create bubbles.
It is easier on a small painting as you can just go across from one end to the other without creating a fuss.
The motive is to apply the varnish evenly and with as thin a coat as possible.
Usually there is always a tendency to over coat the painting leaving it with uneven layers and a disturbing glossy look.
If you have a big painting to varnish, it is better to section out and working on it one by one.
Do not attempt to retouch once you have apply the varnish onto the paintings.
Next, put the varnished painting at a location in which the lights are spot on the varnish.
Look for any spot that you may have unintentionally missed during you varnishing work.
Find a dust free location to place your painting side up and retouch with varnish if needed.
Be careful not to use too much varnish on the spot that is dull, however you may use the varnish on dry paint.
When the painting seems a little dull as it dries up, it indicates that the varnish is painted with a thick and uneven coat.