Add clear glaze to it.
Maybe use polyurethane over your items.
That would just coat the paint, not make it transparent. Have to add to the paint to change its consistency.
Hope this helps ... it's the chemical make up of the product itself ... either by dilution or by original composition from the manufacturer --
I found this article, it may help: https://www.hunker.com/13411611/how-to-make-transparent-paint