Hi there Abi I have also wondered about this, although with Model Air.
Vallejo Premium on the other hand would be a far more durable surface coating especially if the paint is hydrophilic when cured (doesn’t wet). Vallejo have Material Safety Data Sheets available for all their products -
https://acrylicosvallejo.com/en/safety/
This is the PDF for Premium Color -
https://acrylicosvallejo.com/wp-content/uploads/2020/02/SDS-Premium-Color-2019.pdf
Vallejo Premium Color (RC) is a paint for use with Radio Controlled models (I think in this case it’s also used for mini figures and tabletop gaming where the paint will be exposed to handling conditions and take a few knocks here and there depending on the playing style) and as such can be exposed to environmental conditions where abrasion and exposure to solvents (water) can impact the surface finish so the carrier substrate for the pigments has to be hard wearing, in this case the carrier substrate is a Urethane Acrylate Oligomer -
Here’s a study on
Urethane Acrylate Oligomers, the relevant take away point in the document is this -
The only real possible issue with any paint that is fully cured is that some can contain harmful heavy metal elements as pigments such as Cadmium and Chromium etc, if you can avoid those paints that may contain these elements then you get closer to being safer aquatically.
As Premium Color is a hard wearing paint it’s environmental stability should be fairly high though you can’t discount that if applied as a thin glazed layers it may be easily removed from the surface it is adhered to by the action of say a grazing shrimp or a fish capable of nibbling at it. If you wanted to isolate any paint layers where you are unsure of the pigment properties then you could seal in the paint layers with the Premium Varnish, how obvious that varnish is under water depends on how close they match in refractive index (light bending properties) if they closely match the varnish should be invisible, you get three direct shots at achieving this straight out the bottle - Matte, Satin or Gloss - if neither on their own is wholly satisfactory then combining them may improve things, your going to have to conduct testing on samples before committing to a Varnish.
Hopefully this information is useful to you.
