There are many different ways to finish paintings, depending on your preferences. Some artists varnish their work, some do not. It is extremely important that you test various finishes before applying them to your final paintings. 

TO VARNISH OR NOT?

Varnishes are traditionally removable. Even though acrylics dry fast to a durable and flexible film, there are a number of important benefits to varnishing a piece of work. 

BENEFITS OF VARNISHING

Adjusts and unifies the surface sheen.
Minimizes the collection of pollutants into the paint film.
Protects against surface abrasion during shipping or exhibition.
Boosts the brightness and color saturation.
Provides a uniform sheen.
Protects colors from ultraviolet light. (Any varnish will afford some protection but those with UV inhibitors offer extended protection from color fading)
Allows for easy cleaning without fear of removing or damaging the paint film. 

BENEFITS OF NOT VARNISHING

Can continue to edit your painting without any hassle.
Can still adjust and unify the sheen with clear mediums.
Can still use UV protectants such as Golden Gel Topcoat with UVLS. 

Should you choose to varnish, you would apply an Isolation Coat once your painting is finished, and then apply a varnish of your choosing.

ISOLATION COAT

An isolation coat is a clear, gloss, non-removable coating that serves to physically separate the paint surface from a removable varnish.

The Isolation Coat is used to:

Protect the painting if / or when the varnish is removed by separating the pigmented area of the painting from the solvents used in removal.

Seal any absorbent areas in order to create an even surface on which to apply the varnish.

PRODUCT OPTIONS FOR ISOLATION COATS

Soft Gel Gloss
Gloss Medium
Clear Leveling Gel
Gloss UV Topcoat

Any GLOSS medium can be used as an isolation coat depending on the properties you want...clear leveling gel, soft gel gloss, gloss medium. Gloss products provide the most clarity, as opposed to satin, matte, etc. (It’s a good idea to shoot your work before this stage to prevent glare.)

PRODUCT OPTIONS FOR VARNISH (removable)
Cold Wax
Polymer varnish
MSA varnish
Archival spray (Good for varnishing acrylic, as well as watercolor and gouache)

OPTIONS FOR NO VARNISH (non-removable)

Nothing at all
Any transparent or translucent polymer
Liquitex gloss medium & “varnish”
Soft or heavy gel gloss, satin, matte
Gloss or matte fluid medium
Clear leveling gel
Pouring medium
Gloss UV Topcoat