Thanks! Valejo game ink I just got from Amazon. This is my second mini I’ve used them on and I love them.
Vallejo Game Ink Paint Set (8... https://www.amazon.com/dp/B0016CN5MQ?ref=ppx_pop_mob_ap_share
You can use the 'under-shading' approach with any translucent paint. Vallejo inks. AP Speedpaints. Pro Acryl transparents. or make your own with acrylic inks, flow improver and medium.
This isn't a new technique, only the name is.
https://www.amazon.com/Vallejo-Game-Ink-Paint-Color/dp/B0016CN5MQ
https://shop.thearmypainter.com/us/wp8053p
https://monumenthobbies.com/products/pro-acryl-expansion-set-2-transparents
Washes are probably too low in pigment. Inks would be a better choice. I like these. https://www.amazon.com/Vallejo-Game-Ink-Paint-Color/dp/B0016CN5MQ
Depends on the shape, but I've had some success recently using these https://www.amazon.co.uk/Vallejo-Color-Games-Acrylic-Paint/dp/B0016CN5MQ
They're very rich and striking inks, far more than GW or AP, they might do the job.