What is the fat over lean rule?

Each successive layer of oil paint should contain more oil (fat) than the layer below. This is because oilier layers are more flexible and take longer to dry. If a lean (dry) layer is placed over a fat (oily) layer, the top layer dries first and cracks as the bottom layer continues to dry and contract.

Can I use linseed oil on its own as a medium?

Yes, but use it sparingly. Pure linseed oil slows drying significantly and can cause yellowing over time, especially in light colours. For general painting, a 1:1 mix of linseed oil and turpentine gives a good balance of flow and drying time.

What is damar varnish used for in oil mediums?

Damar varnish (dissolved damar resin) adds gloss, transparency and body to oil painting mediums. It is typically used in glazing mediums at a 1:1:1 ratio with oil and turpentine. It helps glazes dry with a luminous, glass-like finish.

ArtCalcs

Oil Medium Calculator

Calculate linseed oil, turpentine and varnish ratios for oil painting mediums at each stage of your painting.

Total Medium Volume

Painting Stage

How We Calculate This

This calculator divides your total medium volume based on recommended ratios for each painting stage.

Fat over lean progression

Lean underpainting: 1:4 oil to turpentine (mostly solvent)
General painting: 1:1 oil to turpentine (balanced)
Fat overpainting: 3:1 oil to turpentine (mostly oil)
Glazing: 1:1:1 oil, turpentine and damar varnish

Frequently Asked Questions

Related Calculators

Paint Coverage Calculator

Calculate how much artist paint you need for any canvas or surface area based on paint type, thickness and number of coats. Free online calculator.

Colour Mixing Calculator

Work out pigment ratios to mix a target colour from primary colours by volume or weight. Covers acrylics, oils and watercolours.

Paint Dilution Calculator

Calculate the correct dilution ratio of paint to thinner or medium for your painting technique. Covers acrylics, oils and watercolours.

Palette Calculator

Plan how much of each paint colour to squeeze onto your palette for a painting session. Avoid waste and never run out mid-painting.

Colour Wheel Calculator

Find harmonious colour combinations using colour wheel theory including complementary, triadic, analogous and split schemes for artists.

Last updated: February 2026

All calculations are estimates. Always verify quantities before purchasing materials.