Mixing oil paint with white spirit is a common practice in oil painting, primarily done to thin the paint for various effects, such as creating washes, underpaintings, or increasing flow.
The Basics of Thinning Oil Paint
White spirit, also known as mineral spirits, acts as a solvent that breaks down the oil in the paint, reducing its viscosity. This allows the paint to spread more thinly and dry faster than using oil mediums alone.
How to Mix
Typically, white spirit is added directly to the oil paint on the palette.
- Start Small: Begin by adding just a few drops of white spirit to a small amount of paint.
- Mix Thoroughly: Use a palette knife or brush to thoroughly mix the solvent into the paint until the desired consistency is achieved.
- Test Consistency: Test the thinned paint on a scrap surface to see how it flows and covers. Add more white spirit gradually if you need it thinner.
Caution: Adding too much white spirit can break down the paint binder (the oil) too much, resulting in a weak, brittle, or matte paint film that may not adhere well or could crack over time.
Important Considerations & Potential Issues
While white spirit is effective for thinning, it's crucial to be aware of potential issues, especially when combining it with other painting mediums or techniques.
Instability When Mixing Mediums
As noted in painting advice, "It's not advisable to mix mediums as they may dry at different rates and that could potentially cause instability between layers." This warning is highly relevant when using white spirit (a solvent thinner, often considered a type of medium or used in conjunction with them) alongside other mediums like alkyd-based products (e.g., Liquin) or traditional oils.
For example, mixing or layering paint thinned heavily with a fast-evaporating solvent like white spirit with paint containing a fast-drying resin medium could lead to complex drying scenarios. If a layer thinned with white spirit is applied over a layer containing a fast-drying medium that is only surface-dry, or vice-versa, the different drying rates can create stress within the paint film.
- Different Drying Rates: White spirit evaporates relatively quickly, leaving behind the oil binder. Oil mediums, especially those with added resins, dry through oxidation and polymerization, which can take longer or cure differently.
- Layering Issues: Applying a fast-drying layer over a slow-drying layer violates the traditional "fat over lean" rule and can trap the lower layer, leading to wrinkling, cracking, or poor adhesion. Conversely, even applying a slower-drying layer over a layer thinned with a fast-evaporating solvent requires ensuring the underlying layer is sufficiently cured.
Table: Thinners vs. Mediums
| Type | Primary Function | Example(s) | Potential Issues (relevant to mixing/layering) |
|---|---|---|---|
| Thinners | Reduce viscosity, aid cleaning, evaporate quickly | White Spirit, Distilled Turpentine | Over-thinning can weaken paint film. Different drying rates can cause instability when layered with other mediums. |
| Mediums | Alter consistency, flow, gloss, texture, drying time | Linseed Oil, Stand Oil, Alkyd Mediums (e.g., Liquin) | Mixing mediums with drastically different drying/curing rates can cause instability between layers. |
Practical Tips for Using White Spirit
- Use white spirit sparingly, especially in upper layers of a painting. Follow the "fat over lean" principle: use more solvent/less oil in underlayers ("lean") and less solvent/more oil or medium in upper layers ("fat").
- Ensure layers are adequately dry before applying subsequent layers, particularly when using different thinning or medium approaches.
- Consider using an artist-grade, odorless mineral spirit if the smell of regular white spirit is an issue.
- White spirit is also excellent for cleaning brushes and palettes after painting with oils.
In summary, mixing oil paint with white spirit is done by adding small amounts to the paint to thin it. However, artists should be mindful that mixing or layering paint thinned with white spirit alongside other mediums can lead to instability due to differing drying rates, as highlighted in painting guidance.
