I was asked;
"So my gallery wants a nice even finish, like that of a varnished piece, on every piece going up on the walls. How do I get that if I am not to varnish a piece for 6 months to a year after I finish it?"
All galleries want that. Here's the best suggestion I can give you. I don't think there is any great harm coating the paintings with Liquin but I think a better fix is to spray them with retouch varnish after they have dried for a day or two. DO NOT use enough that the varnish pools on the surface of your new painting, otherwise it may actually dissolve the paint. This problem goes away after the painting is dryer but I advise you to never let that happen.
It is best to do that in a couple of thin applications. But this is only temporary and the painting should be final varnished at a later date. Several commenters have asked me how I deal with that. The short answer is, often I don't. This is a problem I have discussed with my artist friends and they all seem to do about the same thing, retouch and then out the door. I cannot possibly sit on all my work for a year and then varnish it.
If I do get a chance to varnish a painting that hasn't sold or I am visiting a client who has one of my paintings I will varnish it. I do that with a brush and with the painting lying flat. Keeping it thin is good too, pools of varnish will show on the painting. Matt varnish is a crime against nature. It KILLS your color.
I am thinking that I will write up a page to be included with the painting in an envelope that is stapled to the stretchers describing to the client that the painting needs to be varnished and how to do it. When I do I will publish it to the blog so you all can copy it of and use it too.I often don't know who has my paintings as they are sold through dealers.