What mediums do
A medium is mixed into oil paint to alter one or more of its properties: handling and flow (how the paint moves off the brush), drying time (faster for layering, slower for blending), body (lean and fluid for glazing, bodied for impasto), and finish (matte to gloss). You do not need a medium to start - paint can be used straight from the tube - but mediums give you control over these once you know what effect you are after.
Choosing the right medium
Match the medium to the technique. For glazing, use a lean, fast-drying medium that thins the paint to a transparent film without losing adhesion. For impasto and texture, a bodied medium adds structure and holds brushmarks. For general handling, an all-purpose medium improves flow and levelling across a whole painting. The traditional "fat over lean" rule keeps successive layers flexible: increase the medium (or oil) ratio in later layers so they dry more slowly and do not crack over the leaner ones beneath.
Varnishes: protection and finish
A varnish is the final, sacrificial coating applied over a fully dry oil painting. It evens out the sheen (oil paintings often dry patchy - glossy in darks, matte in lights), saturates the darks back to their wet look, and shields the surface from dust and abrasion. Because it sits on top of the paint film, a varnish can be removed and replaced by a conservator without disturbing the painting - which is why it should never be mixed into the paint itself.
When to varnish: wait until the painting is thoroughly dry - generally 6 to 12 months for a normal oil painting, longer for thick impasto. Varnishing too early traps solvent and risks wrinkling or yellowing. A retouching varnish can be applied earlier for temporary protection and sheen, with a final varnish once the paint is fully dry.
Why Michael Harding mediums and varnishes
The Michael Harding range includes the solvent-free Miracle Medium, a versatile all-purpose medium that improves flow and levelling without the odour and handling concerns of solvent-based options, alongside a full range of oils, mediums, varnishes and primers. Browse the complete mediums and varnishes range, or read the Mediums Guide for detailed guidance on choosing and using each one.
Frequently asked questions
What are oil paint mediums used for?
Mediums modify the handling, drying time and finish of oil paint. They can thin paint for glazing, increase flow and levelling, accelerate or retard drying, add body for impasto, or alter the final sheen from matte to gloss. A medium is mixed into the paint rather than used to clean brushes.
What is the best medium for oil painting?
There is no single best medium - it depends on what you want the paint to do. For glazing, a lean, fast-drying medium thins the paint transparently. For impasto and controlled drying, a bodied medium adds structure. Michael Harding Miracle Medium is a versatile, non-toxic all-purpose medium that improves flow and levelling without solvents.
Do I need a medium to paint in oils?
No. You can paint with oil paint straight from the tube, thinning only with a little solvent for underpainting. Mediums are optional modifiers - you add them when you want to change how the paint handles, dries or looks, not because the paint is incomplete without them.
What is the difference between a medium and a varnish?
A medium is mixed into the paint while you work, altering its properties. A varnish is a final, protective coating applied over a fully dry painting to even out the sheen, saturate darks and shield the surface from dust and abrasion. They are not interchangeable: never mix varnish into paint.
When should I varnish an oil painting?
Wait until the paint film is thoroughly dry - typically 6 to 12 months for a normal oil painting, longer for thick impasto. Varnishing too early traps solvent and can cause wrinkling or yellowing. A retouching varnish can be used earlier for temporary protection and sheen evenness, with a final varnish applied once fully dry.
What is Michael Harding Miracle Medium?
Michael Harding Miracle Medium is a non-toxic, solvent-free all-purpose medium that improves flow, levelling and drying behaviour of oil paint. It can be used throughout a painting without the strong odour and handling concerns of solvent-based mediums. See the Miracle Medium range for the full detail.