Getting the right eco-wood treatment can be difficult. Not many producers make a gloss finish that works as easily as conventional paint manufacturers. This is because natural oils take longer to cure that high solvent content ones, so there is a trade-off between paints with high embodied energy and VOCs and those with natural ingredients and lower natural VOCs. Remember that our bodies and nature are built to cope with natural VOCs (they are present in any oil) and those associated with the pertochemical industry that are alien to us.
Satin / eggshell finishes though are much easier to get with natural paints. These are mostly water based and give an excellent finish, however there are differences between manufacturers. Auro produce a great range of Matt Silk (and Gloss) paints based on orange and linseed oils, whereas Green Paints is based on Soya, whilst EarthBorn have managed to create an eggshell that is totally water based without any oils (ProAqua Eggshell).
So to the most important considerations.
For cost – Green Paints is the most competitively priced. A good quality paint, but it does take some time to cure, so I would not recommend in areas like door jambs, windows or on surfaces that will have heavy items on. I would also only use their semi-gloss. Also only available in a very limited range of colours.
For eco-credentials – Auro is a great manufacturer (carbon zero) that has a good range of paints. They even produce a natural paint suitable for exterior use – their High Gloss 935 paint. This does take a long time to dry to be aware that you will need to leave around 6 weeks to cure. A great range of colours though in their 250 and 260 paints.
For quick drying – EarthBorn ProAqua Eggshell is a must – dry in about 20 minutes and no smell at all. Totally VOC free.
On untreated wood – I would probably use the Osmo Woodwax Creativ range here. One coat for a translucent finish and two for an opaque one, but it does need to go onto untreated wood.
For application on pre-painted wood (not inc. Osmo), give the surface a gentle rub over with sand paper to create a key for the paint to adhere to and then you can either add an appropriate undercoat followed by a top coat, or (most people will just) add a top coat.
For fresh wood either use Osmo, or if using other types of paint make sure you seal any knots with a Shellac, then add an primer, undercoat and a top coat. EarthBorn ProAqua will act as a primer if watered down by 20%.