When you use acrylic paints very watered down the finished art piece can be protected with a sealant or varnish.
Depending on your painting style, you MIGHT not need a sealer, but if you do, there are several brands that provide high quality sealers and varnishes for artists.
Liquitex make a professional varnish that you can look at here:
Jacksonsart liquitex professional high gloss rigid varnish
If that does not suit your purpose you can search that website for ‘Varnishes’ and you will be presented with lots of different types, suitable for acrylics as well as varnishes for oil paintings.
Some artists like to use paints very thinly, more like a stain, to allow the surface to show through, for instance on wood or metals. You might want to make watercolour-like effects on paper and show the colour underneath. This is certainly possible with acrylics but an understanding of the paint and how it behaves is useful because different colours behave differently from one another.
Overthinning can compromise the integrity of the paint, causing it to separate and become weak. If you want a transparent effect it may be better to use a gel to extend the paint while providing a stable medium.
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Matt and gloss finishes are available and some of the extending gels that can be mixed with paints can change the final finish making it high gloss or give it an eggshell sheen and others can make the surface matt.
When our Outlines paints are used straight from the tube or only very slightly watered down they dry with a soft gloss finish and when completely dry, they are tough and keep their colour well.
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