I've met many potters who struggle to decide how to glaze their pots. At HPG we have over 50 glazes, so there are plenty of glazes to choose from, and that might be part of the problem. There are so many choices that people can't make up their mind. Following are some suggestions that I hope will make your choosing a little easier. I should also add that the following information is really about how to prepare to glaze your pots and not the actual techniques for glazing. Those are best handled through demonstrations or videos.
First, start a notebook. I have a longer blog about that right here: www.jonrawlingspottery.com/blog/keeping-a-notebook I draw simple pictures of each pot and include basic information about what clay I used to make it and what I may have done to decorate it before glazing, especially if I carved it. I usually wait until I have at least 10 large pots before I start glazing them. I number each pot on the bottom of the foot and put that down in the notebook since it's easy to get similar pots mixed up. I lay them out on a table and begin thinking about how to decorate them. I take my time with this. I try to get the juices flowing by thinking about simple things like how to glaze the inside of vases. Okay, I'm usually going to use a white glaze like Glossy White or Miller White so I write that down. With large bowls I start by deciding whether or not to use a wax resist pattern on the inside or outside. All of these decisions can be tweaked as I glaze, but using a notebook helps me organize my thinking, decide what I want to do, and keep a record of those decisions.
Second, think about the clay you're using. As I draw each pot in my notebook, I note above it what clay I used. After numbering each pot, I start with pot #1 and start thinking about how I might glaze it. Glazes look different on different clay bodies. If I use Butter Yellow on Rod's Bod, it looks like burl wood; if I use it on porcelain, it looks light yellow. After some experience, you'll begin making certain shapes with certain clay bodies with specific glazes already in mind. For more detailed examples about how to glaze different clay bodies, see my blog on black and brown stoneware: www.jonrawlingspottery.com/blog/black-and-brown-stoneware
Third, think about what glazes are appropriate for your pot's form and function. I'm often surprised by the glazes some potters use on their pieces. For instance, I've seen potters carve a piece with meticulous detail only to cover it all up with a thick Shino glaze. Or they use a glaze that seems inappropriate for a functional piece. I'm no expert on what glazes are more food safe, but it certainly seems we need to give more attention to this at our potters guilds. I didn't even know it was an issue the first year or so I was making pots, so I sold small bowls to unsuspecting customers that had copper or cobalt or chrome in the liner and I even sold them bowls with crystalline glazes inside. When I started learning more about some glazes being food safe and others not so much, I asked more experienced potters and teachers about what glazes were appropriate to use. Everyone waved off my concerns with comments like "Oh, I heard it's fine" or "Don't worry about it. Just don't store spaghetti sauce in it for a week." Maybe we should send examples of all of our glazes to a lab so we can be sure how much stuff might be leaching into food from our glazes. Commercial makers are held to high standards because it could impact public safety; maybe we should hold ourselves to the same high standards as well. As an intermediate step, I try to use only glossy glazes as liners for small bowls, especially glossy white. I'm also doing experiments on clear glazes that won't craze as much since we have several glazes based on a single chun recipe that tend to craze dramatically.
Fourth, think about how you'll apply the glazes and in what order. If I dip a pot in Butter Yellow it will be a glossy light yellow; if I spray it, Butter Yellow will be a matte light brown or tan depending on the clay body. Some dark clay bodies like Black Mountain will turn every glaze dark brown if they're applied too thinly. A second coat is necessary to get any of the original glaze's color to show up at all. Some glazes look awful on porcelain but on darker clay they look terrific with lots of variation in color depending on the thickness. I use several techniques to apply glazes to pots. With bowls I tend to pour glazes inside to give it a thick layer. After waiting a day for the glaze to dry. I turn the bowl upside down and spray the outside. If I've made a wax resist pattern outside, I'll pour the glaze. Wax resist doesn't work that well with spraying as the glaze tends to build up on the edges and stops shedding off. I'll then turn the bowl over and apply another glaze inside using techniques such as spraying, spritzing, or different designs with a ketchup bottle or rubber syringe. I also consider what order I'll use to glaze each pot. For instance, I glaze the inside of a bowl first. I want a thick layer so I usually pour a glaze inside, swish it around for a few seconds, and pour it out. If I spray a glaze inside, I've found it difficult to trail glazes over the sprayed layer. The sprayed glaze usually is fluffy and the trailed glaze will sit up on the glaze and often flake off. I also need a thick enough glaze layer to get some of the effects I'm going after, especially on darker clay. I'll usually wait a day for the pot to dry and then turn it upside down on a banding wheel and glaze the outside, usually by spraying. If I'm spraying or trailing another glaze on the inside, I'll turn the pot right side up and glaze it the same day. No need to wait another day. Since it takes so much time to set up the spray booth and then clean it after, I always wait until I have at least 10 pots before I start glazing. I glaze the insides of all of them, wait at least a day, then glaze the outside and finish up the inside. I organize pots according to the glazes I'm going to use. If I have four bowls that need to be sprayed outside with Butter Yellow, I'll spray them one after another until I'm finished. Then if I have two that need Sky Blue Chun I'll spray them next. After I'm done on the outside, I'll reorganize them according to what glazes I'll need on the inside, if I'm spraying them. So some of them will need to be sprayed with Oxblood, some with Pete's Cranberry, and so forth. I plan on writing a blog about how to spray pots so I'll say more about spraying in the future.
Fifth, prepare pots for glazing. If I have the time, I completely wash my pots after they've been bisqued, especially porcelain. I do some sanding on all of my pots and they typically have quite a bit of clay dust on them. Removing the dust is imperative if you want the glaze to adhere well. I'm especially careful with pots that I've carved. I'll use a toothbrush and water to remove all of the dust from recesses that might cause the glaze to not adhere to the pot. If I wash a pot like this, I have to wait at least a day before the pot is dry enough to glaze. If the pot doesn't have much dust on it because I only lightly sanded it, I'll use a sponge to wipe off all of the surfaces. I'll wait an hour or so until the pot has had some time to dry before glazing it. When pots are bisqued, they are strong enough to handle more aggressively and yet are still porous since they're not fully vitrified. Glazes are a slurry of powdered minerals mixed in water and very little material in glazes is soluble. When applied to a porous bisqued pot, the water is absorbed into the body of the pot leaving a thin layer of powdered minerals on the surface. If the pot is too saturated with water, a glaze applied to the other side of the clay body will not absorb much water and will leave a layer of glaze that's too thin. The thinner the walls of the pot, the more important it becomes to wait until the inside of the pot is dry before glazing the outside. It's already difficult to get a thick enough layer of glaze if the walls of your pot are very thin since the walls cannot absorb much moisture before becoming fully saturated.
Sixth, prepare your glaze. Start by taking a metal whisk and stirring the glaze from the bottom. You should use a motion that not only goes around but also begins lifting the material up toward the top. Whether you're dipping a pot into the glaze or scooping it into a pitcher, the glaze you're using will come from the top of the glaze. That's why it's important to make sure you mix the glaze until the stuff on the bottom has worked it's way to the top. HPG has several glazes that take some time and arm power to get thoroughly mixed. If you stop mixing too soon, the glaze will be watery and won't have all the material in it that you need. After the glaze is thoroughly mixed, I sieve the part I'm going to use. The only exception to this is if I'm glazing a large vase and need to dip it into the larger bucket. Otherwise, I always sieve the glaze to remove debris that's fallen into the bucket, material that hasn't mixed in well, and even pieces of plastic from the bottom of the bucket that have been shaved off by the whisk. This is worth the extra effort since it gives a more consistent result. If you've ever used unsieved glazes, you know how often debris can cause blemishes in the glaze. While I think sieving is usually the best thing to do when preparing glazes, it's absolutely essential when preparing glazes for spraying. I use a pretty fine stainless steel sieve that I picked up at Williams-Sonoma. You might think that sieving is a waste of time, but I've seen how much time people waste when their spray gun gets clogged up and they have to take it apart to remove the debris. A few simple steps will save you more time in the end and help you get a better result.