Determining the difference and making a decision between glass and acrylic glazing or extras like UV-protection and non-glare is often a less obvious choice than many may think. I hope to make the decision a bit clearer and easier!
Acrylic is commonly referred to as plexi-glass (or just plexi). Like Kleenex or Xerox, Plexiglas is actually a registered trademark that has crept into standard English vernacular. In reality, of course, Plexiglas is only one of many brands.
There are some immediate and distinct advantages to acrylic, making it an attractive option. Acrylic is quite shatter-resistant, meaning it won't shatter into thousands of pieces during the next earthquake (or if you drop it). This means it's much safer to use if you're having to handle glazing yourself. It's also much, much lighter than glass—by 50% or more depending on the thickness you choose. This not only makes carrying around and hanging larger pieces easier, but it affects things like shipping costs if you are having your acrylic cut elsewhere. Anyone who travels to art shows or fairs will see this as a life-saver for packing and carrying around your artwork while still having that added protection.
Acrylic also lets in more light (90% vs. around 80%) than standard glass, making it clearer and giving better light to view your work. While standard acrylic has little inherant protection against harsh ultra-violet (UV) lights, options exist to counter that (as you will read later).
So those are the advantages. It's easy to see where acrylic would be the best option, but there are negatives, right? Well, for one acrylic is extremely scratch-prone. That means special cleaners and cloths, and extra care in handling. One large scratch can mean an end to your glazing. Scratch-resistant acrylic exists, but may be hard to find. Acrylic is static-susceptible too, which is not good for artwork like chalk or charcoal. It also picks up dust more easily for that reason. Acrylic is also not as rigid as glass, and therefore has the potential to bow. Lastly, it can be more expensive than standard, non-UV glass. A deciding factor when adding up the costs of custom framing.
Glass has been around for a long time. It's well known, time-tested and reliable. Looking at the advantages of acrylic, the disadvantages of glass are immediately known; it can be dangerous, easy to break, and heavy. Often the edges will not be smooth, so one slip of the finger when handling can lead to blood and band-aids. Shipping is a problem not only because of weight, but because it cannot travel reliably with any carrier. Even small pieces packed well are not immune to being shattered in one bounce of the delivery truck. Another negative to standard glass is a green 'cast' or tint that is seen depending on the thickness and lighting conditions, making it a bit less clear than standard acrylic.
On the flip side, for those not doing any shipping or handling of their own glass, it's still an excellent choice. It's a bit cheaper than acrylic, and you can clean it without as much worry.
So now we've covered the standard versions of both glazings, but what about special coatings and conservation properties?
Both acrylic and glass are available with UV protection options. This is absolutely necessary if you are framing using other conservation materials. Without it, not even the best mats will completely protect your work, as light will do some of the worst damage. Please remember that even the best glazing will provide a maximum of 98% UV protection. It's best to keep your work out of direct sunlight no matter the materials used in framing, as that 2% will still add up over the years. The slight downside to UV protection is that it does add a bit of a yellowish tinge (rather than the green of glass) to both glazings. This warmer color will probably not be noticeable to the average person unless comparing glazings side-by-side.
NON-GLARE & ANTI-REFLECTIVE
If you need something non-reflective, you have two options: Non-glare, which has one side chemically 'etched' to diffuse light, and anti-reflective, which has an optical coating applied to it (like a camera lens). The downside to non-glare, unfortunately, is that it reduces contrast and sharpness to your work, giving it a fuzzy or matte look. Depending on the type of art, this may work well; however, those needing excellent light without the glare, will want to look at anti-reflective glazing. Typically used in museums or galleries, it's the most expensive option you will find. Tru-Vue's Museum Glass is a good example of anti-reflective glass.
Keep in mind that non-glare and anti-reflective glass may not, by default, be UV-resistant. You will have to make sure you are getting that option if you need conservation quality.
If you are concerned about price but want clear, archival glazing, your best option would be a standard, UV-resistant glass or acrylic. You will still get conservation-quality glazing but without the extra cost of non-glare. You'll just have to be a bit more picky about the location of your work to prevent glaring light. If you are able to, pick up a few samples and try them under various lighting conditions. Whether to choose a non-glare or clear glazing can be a simple matter of preference.
Hopefully you've gleaned from this article enough information to understand the main differences between glazings and their properties. You may very well encounter different terminology and technologies, but it's a safe bet that you can pin it down to one of the aforementioned combinations. If you are not framing yourself, be sure to take into account the advice of your custom framer. They may know specifics about your piece or situation which are not covered here. Good luck!