Best Thinner for Sign Painting Enamels
Paint thinners, or reducers, are a key part of any sign painter’s kit. They not only get our lettering enamels into a workable consistency that flows off your brush just right, but you also need them to clean the paint out of your bristles before storing them between jobs. With so many options out there, the question often comes up: Which is the best to use?
Turpentine vs. Mineral Spirits
Turpentine is a classic choice for thinning and reducing sign enamel.
Turpentine and mineral spirits, sometimes called white spirits, are the two most recommended paint thinners by active sign writers. For good reason, too: they work, they’re readily available, easy to find, and in terms of toxicity, they’re on the lower end of reducers one could pour into their paint.
Turpentine is a solvent distilled from pine trees, so it has points for being a sustainable and renewable product. It also smells just like pine, which is nice if you’re into that. Precisely because it’s made from pine, of which there are many species, some people find it an intolerable irritant. It’s a little bit “hotter” than mineral spirits, which means it’s a little stronger and has more kick for different materials. This is both a blessing and a bane.
I find turpentine to add a little bit of drag to the paint. Some like this, others can’t stand it.
Odorless mineral spirits are the distilled byproduct of the petroleum industry, meaning they are a good, efficient use of materials but are not renewable. They’re relatively mild compared to other solvents but are still toxic if inhaled or if they come into contact with skin. Odorless mineral spirits are usually less expensive per ounce than turpentine and neutral in terms of smell, usually giving it the advantage.
I’ve never noticed a difference in end result quality from either.
Lacquer Thinner vs. Mineral Spirits
Avoid using lacquer thinner in your shop unless specifically required by a material.
Lacquer thinner is hot, hot, hot! It’s a mix of some pretty nasty solvents like xylene, acetone, and toluene, to name a few, all of which will melt your lungs out and probably give you cancer.* Seriously though, unless you’re in an industry or using a product that specifically calls for lacquer thinner, avoid it to the best of your ability - and 1,000% use PPE if you have work with the stuff.
Some well-known sign writers, my grandpa included, will recommend you use lacquer thinner to wash out your brushes pre and post-painting. Steve Kafka is even such an advocate of this method that his signature brushes, the Kafka Kwills, come with bare wood handles because he knows the lacquer thinner will eat away what varnish is there if they weren’t raw. If lacquer thinner will eat away cured varnish, I shudder to think what it would do to the glues holding the bristles in place or the bristles themselves.
Stick to odorless mineral spirits.
*Exaggeration for dramatic effect, but honestly, probably not far from the truth.
Lacquer Thinner vs. Turpentine
Turpentine. Hard stop. See above.
Turpentine is a great stand-in for those times a sign painter recommends you wash out your brushes with lacquer thinner. It’s hotter than mineral spirits but less toxic than lacquer thinner. Turpentine can be on the more expensive side, but all of the organs lacquer thinner can f up are worth more than a few saved pennies.
Either way, wear your damn respirator.
Brand-Specific Reducers
Each of the big three enamel paint brands, 1 Shot, Alpha 6, and Ronin, recommend that their paint be thinned and reduced with their proprietary reducers. On the surface, this makes perfect sense; they formulated the paint, so they probably formulated the ideal reducer to pair with it. In many cases, they’ve also formulated reducers that help in extreme cold and hot temperatures. Here’s the rub, though: after enough time, most of us are going to end up with paint from all three brands in our shop, which means we would need to keep in stock, at minimum, six different reducers! Granted, one could probably use 1 Shot Low Temp instead of Alpha6 Low Temp, but I think the general point is that turpentine and mineral spirits can be used in all enamel paints, reducing (see what I did there?) the amount of thinners one would need to keep in stock.
Our Picks
Best All-Around: Odorless Mineral Spirits
It’s hard to go wrong with a good quality odorless mineral spirit. It’ll thin your paint without affecting adhesion or gloss if done properly. It’s lower on the toxicity spectrum than some of its alternatives, and you can find it in any art supply or hardware store.
Two things to be aware of, however:
Make sure to use high-quality odorless mineral spirits and avoid the “green-washed” options.
Just because it is odorless does not mean it isn’t off-gassing toxic fumes into the air for you to breathe. Wear a respirator even if you can’t smell it!
Best Combo: Turpentine & Mineral Spirits
Turpentine is just a bit “hotter” than odorless mineral spirits, making it a great option for cleaning the oils out of your brush before you start painting, and getting the paint out of your brush before you prep them for storage. The fact that it is a little bit stronger and has a noticeable odor to it also means it is a bit higher on the toxic spectrum, meaning one needs to be even more careful with turpentine and be sure to wear a respirator.
A bonus for this combo is that if you get a little turpentine mixed into your mineral spirits, or vice versa, it’ll be no harm, no foul.
I go back and forth about what I like best between these two, but it is worth noting that because I can smell the turpentine, I find myself wearing my respirator more. 🤷♂️
Dishonorable Mention: Hardware Store Paint Thinner
Avoid this stuff. You can use it in a dire pinch if you have to, but it should be avoided. The thing with hardware store paint thinner is there’s no true definition or standard for what it is, meaning each brand could have a different mixture of solvents, and you have no way of knowing what you’re putting in your paint. Sure, it’s cheaper than everything else, but the risk isn’t worth the savings.
