Glossiness aka. sheen aka. reflectiveness:

• Matte: finish with a low or no shine
• Semi-matte: finish with a tiny shine
• Semi-glossy / Satin: finish with a slight shine
• Glossy: a finish with a high shine

A matte finish makes taking photos of miniatures easier as the light doesn't bounce off the paint. But you must paint all the highlights which can be tedious.

A glossier finish allows the environmental light to bounce off the paint and thus naturally makes the miniature look more vibrant without additional effort when viewed in person, but it can be difficult to take good photos.

Different paints have different glossiness levels. Glossiness can vary even within the same brand according to paint range e.g. Scale75 Scalecolor is matte while Scale75 Fantasy and Games is satin. Sometimes, but rarely, paint glossiness can vary even within the same paint range according to pigments used for particular colors. But generally, the paint range is the most important factor as the majority of glossiness comes from the paint formula medium.

I find it annoying to use paints with different glossiness on a single miniature. Even if you were to varnish the miniature in the end, it is tedious to see how it will look if half of the miniature shines and the other half is matte.

I have done simple tests on the glossiness of the paints; I simply painted some primed squares and sorted them according to perceived glossiness. The results are as follows:

• Matte:
  • AK Interactive 2nd Gen
  • Scale 75 Scalecolor
• Semi-matte:
  • Scale 75 Artist Colors
  • Scale 75 Instant Colors
  • Vallejo Model Color
• Semi-glossy:
  • AK Interactive 3rd Gen
  • Army Painter
• Glossy:
  • Game Workshop Citadel

For example, I wouldn't mix Scale75 Scalecolor and Games Workshop Citadel paints on a single miniature, although I could mix Scale75 Scalecolor and Scale75 Artist Colors or Games Workshop Citadel and Army Painter paints.

Matting Agents

Here are some "mediums" that I've tried to add to paints to make them more matte.

The testing process:

1. Prime a square with Vallejo Gloss Black primer.
2. Paint the square with the medium using 3 thin coats.
3. Place 3 drops of the medium to the middle to form a thick blob as well.
4. Let it dry for an overnight.
5. Compare the sheen with the rest of the squares.
6. To test the viscosity, I just pour a drop of it on my finger and squeeze it.

Retarders and Glossiness

Paint retarders can affect the glossiness of the final result.

• Green Stuff World Brush Retarder: medium feels like your usual paint, barely even makes the paint dry slower but a matte paint keeps matte finish.
• Scale75 Retarder: really runny medium, makes paint runny too, somewhat slows drying time and doesn't affect paint finish too much.
• Vallejo Retarder Medium: really thick medium, slows the drying time considerably but leaves a very glossy finish.