"I have just completed my third portrait and decided to varnish it to see if it brightened the colors even more. When I finished the coat of varnish I noticed a very slight smudging of one of the colors. The painting had been dry for three days before varnishing and I followed the instructions on the bottle, and did not over brush. I am using Atelier paint and an Atelier Satin Medium Varnish. Any idea where I went wrong?" -- Kooky
Given that Atelier Interactive acrylic is formulated to "unlock" or reabsorb when moisture is applied, I suspect there must have been a bit of thicker paint that was still wet underneath and the varnish unlocked it, causing it to spread? Acrylic paint can feel touch dry but that doesn't necessarily mean it's cured (thoroughly dried all the way).
I emailed Chroma USA to ask how long they recommend to wait before varnishing. Jennifer VonStein, Chroma's Resident Artist, responded with some very helpful information. (I've highlighted a few crucial bits.)
"When using a water-based varnish, like our Satin Medium/Varnish, on top of an Atelier Interactive painting, Chroma Inc recommends waiting until the work has cured. Generally, I wait at least two weeks, but the cure time is affected by humidity, temperature, what mediums were used and how thickly the paint is applied. So if it is humid, an impasto painting and I used a lot of Slow Medium, I may even wait a month.
"If the varnish reactivated paint, then that layer wasn't fully dried. It is important to note that when varnishing, an isolation coat is recommended. We suggest that you seal the surface first by applying one coat of Fast Medium/Fixer or diluted coat of Binder Medium prior to varnishing.
"Water-based varnishes are tricky to apply and not removable if you dislike the effect, so we suggest they should only be used by artists who already know them well and are not experimenting. We recommend and prefer our Chroma Solvent based varnishes, which can be used on all our Chroma paint brands, including Atelier Interactive.
An info sheet on varnishing with Chroma varnishes can be found online through Chroma Link. Remember, touching a finger onto the paint and it coming away clean isn't a true way of knowing if a painting is cured. Be patient and, if in doubt, rather don't varnish just yet.