Genuine slate is the heaviest, most dense material used on billiard tables. No other material will give the ball a true, almost frictionless roll. Italian slate has been the choice of professional players for years, because it is dense with excellent moisture content. This allows the installer to tighten it more securely without cracking. Most important, it vibrates less with a hard shot; giving the ball a more accurate roll. Why? The climate in Italy millions of years ago and the depth of the mines. Italians have been mining slate for 200 years – the mines are now very deep. Brazilian slate is mined closer to the surface; giving us a slightly lower moisture content. It is certainly much less expensive to quarry. Chinese slate is brittle and much cheaper to quarry and finish. These differences are most noticeable when you hit the balls hard; such as the break, breaking a cluster, drilling a ball into a pocket while stopping the cue ball, etc.
What does this mean to you? As in most of this discussion, if you are a poor player and do not intend to improve; not much. If you want to be a serious player, spring for the Italian slate. However, make sure it really is Italian. Giving Chinese slate a name that ends in a vowel does not make it Italian. If you are buying an inexpensive table, expect that you are getting Chinese slate, and try to at least upgrade to Brazilian slate. If it’s a really cheap table, stay with the Chinese slate. If the table itself is not capable of performing well, improving the slate is not going to help appreciably.
Professional quality tables will generally feature slate between half and one inch thick, and that is the finished thickness. Don’t fall for this scam: “Yes, that’s only ¾ inch now, but it was one inch thick before it was trimmed. Just like a 2×4 isn’t 2 inches thick”. Not true: one inch slate is one inch thick, and that doesn’t count any framing that is glued to it. The best tables will have a wood or composition frame glued to its edge – making it easier for the installer to attach the cloth, and forming a better base through which to bolt the rails. Slate framing also makes the table quieter, and reduces vibration, making the balls roll more consistently. Composition framing will not warp as easily as pine or poplar – and is usually more flat and level during initial installation. That allows the slate to be leveled with a minimum of shimming, for a more stable base. However, the composition material will not handle multiple stapling as well as solid wood. After about fifteen recoveries, you will have to replace the framing, or leave it there and stop stapling. In a home environment, that should be in about one hundred to three hundred years. In a busy pool hall, however, that could be in only seven to thirty years. In commercial environments, then, we would generally recommend poplar framing.
There is also a big difference between actual framed slate and slate framed, or even slate on a slate pad. Sitting unframed slate on top of a piece of particle board does not make it framed slate. Attaching the slate permanently to the framing makes them a single piece. The framing cannot warp or sag because it is part of the slate. Shimming to fine-tune the level can be done between the slate framing and the table’s frame. Actual unframed slate sitting on top of a slate pad can shift, cannot be precisely shimmed, and cannot be tightly stapled to hold the cloth. It sounds similar, but it’s not the same. That is why the Billiard Congress of America requires that only one inch actual framed slate can be used in a commercial regulation table. That’s also why there is no logical reason to make slate thicker than one inch – why would anyone pay extra for a non-regulation pool table? It’s one thing to have a golf ball that you can’t use in a tournament. It’s quite another to have your only pool table be non-regulation!