Two questions get tangled together here. Which varnish matters much less than whether you varnish correctly, and the single most common mistake is doing it too soon.
Here is what varnish is for, the three types, the timing, and an honest answer about whether a paint by numbers canvas needs one.
What varnish actually does
Three things, and it is worth being clear about which you want.
- It evens out the sheen. Acrylic dries to different degrees of gloss depending on the pigment, so a finished painting often has patches that look dull next to patches that look wet. A single varnish over everything makes the whole surface consistent. On a numbered canvas this is usually the main reason to bother.
- It protects. Dried acrylic stays slightly soft and attracts dust, and it is not something you can wipe clean. A removable varnish takes the dirt with it when it is eventually removed.
- It changes the look. Gloss deepens dark colors and increases contrast. Matte does the opposite. This is a real, visible change and not everyone wants it.
What varnish does not do is fix a patchy paint job, hide a printed number showing through a thin coat, or make a painting waterproof enough to hang outdoors.
The timing, which is where most people go wrong
Acrylic is touch-dry in minutes and nowhere near cured. The water leaves quickly; the film keeps hardening for weeks. Varnish over a film that is still coalescing and you can trap moisture, which shows up as cloudiness, or lock in a surface that then moves underneath the varnish.
Allow around two weeks before varnishing. Thin, flat coats need less; anything applied thickly needs more. If in doubt, longer costs you nothing.
The isolation coat, if you use one, can go on sooner — a day or two after finishing for thin paint, a week or two for thick or impasto work. Then wait at least another day, and preferably a few, before the varnish itself.
The isolation coat, which almost nobody mentions
This is the step that separates a varnish you can remove from a varnish that is now permanently part of your painting.
An isolation coat is a thin, clear, permanent layer of gloss acrylic medium applied over the finished painting, underneath the varnish. It does two jobs. It gives the varnish a uniform, non-absorbent surface to sit on, so the varnish goes on evenly. And it puts a physical barrier between the paint and the varnish, so that if the varnish is ever removed, the solvent used to remove it cannot reach the paint.
Between sessions the problem runs the other way. keeping the paint usable covers how to close a pot so it is still good next week.
If something has gone on that you want off rather than sealed in, removing acrylic from a numbered canvas is an honest account of what is and is not possible.
Golden suggests their Soft Gel Gloss thinned with water, roughly two parts gel to one part water. Liquitex suggests one or two coats of their gloss fluid varnish as a barrier under Soluvar. Either approach does the same thing.
Do you have to? No. If you never intend to remove the varnish, you can skip it. But a removable varnish applied straight onto bare acrylic is not really removable, because the acrylic paint and the acrylic varnish are chemically similar enough that the solvent attacks both.
The three types
Polymer varnish, water-based
Thins with water, cleans up with soap and water, low odor, and can be used in an ordinary room. It is removable with a strong ammonia solution, which is a job for someone who knows what they are doing rather than a casual touch-up.
This is the sensible default for most people and most paintings.
Mineral spirit acrylic varnish, solvent-based
Thinned and removed with mineral spirits rather than water. It gives a harder, clearer film that stays removable more reliably over time, which is why it is the conservation-minded choice. Golden's MSA line is the best-known example.
The trade is fumes. It needs real ventilation, not a cracked window, and it should not be sprayed indoors.
Spray varnish
Comes in both chemistries. The advantage is that nothing touches the painting, so there are no brush marks and no risk of dragging paint. The disadvantages are overspray, less control of thickness, and the need to do it outdoors or in a well-ventilated space.
Sprays suit textured and impasto surfaces, where a brush would skip over the high points and pool in the low ones. Brush-on suits flat work, where you want a thicker, more even film.
Do not use hairspray. It appears constantly as a cheap substitute. It is not archival, it yellows, it stays tacky in humidity, and it cannot be removed.
Gloss, matte or satin
- Gloss deepens darks, raises contrast and makes color look more saturated. It also reflects the room, so a glossy painting on a wall opposite a window is hard to see.
- Matte kills reflections and slightly lightens and flattens the darks, because the matting agent is a fine solid suspended in the medium. Applied thickly it can veil the painting slightly.
- Satin is a blend of the two and is the safe choice when you are unsure.
You can mix gloss and matte from the same line to get any point between them. Do not mix across brands or chemistries.
For a painting that will hang on a normal wall in a normal room, satin or matte usually looks better than gloss, whatever the tin suggests.
Which brands
Varnish is one of the areas where the established art materials manufacturers are worth the money, because the failure mode is yellowing over years rather than something you notice in the shop. Product names change, so check the current line before buying.
- Golden make both a water-based polymer varnish and a solvent-based MSA varnish, both available with ultraviolet light stabilizers and both in gloss, satin and matte. The most complete range, and the clearest technical documentation of any manufacturer.
- Liquitex make fluid gloss and matte varnishes suited to isolation coats, and Soluvar as a removable final varnish. Widely stocked and straightforward.
- Winsor and Newton make a satin and gloss acrylic varnish that behave well under a brush.
- Krylon and Montana make spray varnishes that are easy to find and cheaper. Fine for decorative work. For something you want to last decades, use an artists' varnish from one of the first three.
Ignore anything sold as clear coat for cars, metal or plastic. Those turn up in searches for acrylic sealer and they are not formulated to stay clear over an artwork.
How to apply it
- Dust the painting with a soft dry brush. Anything on the surface is about to be sealed under the varnish permanently.
- Work flat, not upright. Vertical means runs, every time.
- Test on a corner if you can, or on a scrap painted in the same colors. Matte varnish in particular does not always look how you expect over dark passages.
- Thin coats. Two thin coats beat one thick one for evenness and for clarity. Let the first dry fully.
- One direction, then the other. Brush the first coat in one direction across the whole surface, and the second at right angles to it. Use a wide, soft, flat brush and do not go back over an area that has started to set.
- For sprays, shake well, keep the can moving, hold it about a foot away, and build up in light passes rather than trying to cover in one.
- Let it dry somewhere dust-free, flat, for at least a day.
Does a paint by numbers canvas need varnishing?
No, and plenty of people never do it. Here is when it is worth it.
Worth doing if your finished canvas has that patchy look where some sections dried glossy and others dried flat. This is common on numbered canvases because the pots vary, and a single satin or matte varnish fixes it completely. It is the most visible improvement you can make to a finished kit for very little effort.
Worth doing if it is going somewhere it will get handled, or in a kitchen where it will pick up grease.
Not worth doing if you are happy with how it looks and it is going straight behind glass in a frame. The glass does the protecting.
Two specific warnings for numbered canvases. Varnish will not hide a printed number that a thin coat of light paint failed to cover — fix that first with a second coat, as in our guide to correcting paint by numbers mistakes. And on an unframed canvas that is still loose, varnish while it is flat and taped down, because varnishing a slack canvas sets the ripples in place.
Once it is varnished and dry, our guide to framing a finished canvas covers what to do next. Every design in the range is also sold in a framed version that arrives pre-stretched, if you would rather skip that part.
Common questions
How long before I can varnish?
Around two weeks for a normally painted acrylic, longer for thick paint. Touch-dry is not cured.
Do I need an isolation coat?
Only if you want the varnish to be genuinely removable later. For a kit painted for pleasure and hung at home, skipping it is a reasonable choice.
Can I varnish over a mistake I painted out?
Yes, once the correction is fully dry. Varnish will not hide the slight step in surface height, but nothing does, and nobody sees it from more than a foot away.
My varnish dried cloudy. What happened?
Usually one of three things: applied too thick, applied in high humidity or cold, or applied before the paint had cured. Matte varnish applied heavily also goes milky over dark colors. A cloudy solvent-based varnish can sometimes be removed and redone; a water-based one usually cannot.
Can I varnish an outdoor sign or a piece for the garden?
Not with an artists' varnish. Those are formulated for interior conditions, and any claim of weatherproofing on a craft varnish will not survive a season of real weather.
Is varnish the same as gesso or sealer?
No. Gesso goes on the bare canvas before you paint, to give the paint something to grip. Varnish goes on at the very end. Our guide to what gesso is covers the other end of the process.
