First and foremost, bloomed chocolate is not ruined. You can temper and re-temper it until Bessie has come back from seeing the world.
Feel better? Good. Oh, you threw it out. Oh, so sorry. (sad face).
Well, moving on, there are a few tempering articles around here. The first and primary one, if you have not found it, is in the right column, under the Alchemist's Notebook.
That goes over the basics of the "how to". You can also look and read the following. I've been told it really helps. It's a little more of the 'whys':
I know a lot of you have trouble tempering. My hope and goal is to show you it really is not that hard (at all), and if you can understand how and why it works (or does not work) it will suddenly be less daunting and much easier to do.
From what I have found is people shy away instantly when they try to read about why it works - they see words like crystallization, and Type V crystals and ....well...freak out and stop listening. For me, it's easy - I'm a chemist. I understand that most people don't think like we (chemists) do (shush).
So let's try this. I'm going to give you basic words. They may or may not be fully accurate, but my goal is to get a concept across to you, and once it 'clicks' you can answer the question above without even thinking about it. I want to get you to 'see' what is happening when chocolate tempers.
Alright, some definitions and concepts are in order.
Sugar and salt form particular shapes on the molecular level. These shapes are crystals. Salt crystals and sugar crystals are different shaped crystals but are both crystals. Good? Good!
Cocoa butter, although it is not sugar or salt, can have a shape too. It can and does form crystals. OK? Good.
Cocoa butter can form (at least) 6 different 'shapes'. Why? Think of it this way.
Sugar is like a baseball (on the molecular scale). If you have a whole pile of them, there is really only one or two ways you can make a stack of them where they are stable. Cocoa butter is shaped more like a the bat (baseball bat, not flying bat). It's long. It is not just a rod. You can tell one end from the other. You can make LOTS (6?) of stable stacks of baseball bats. Some are more stable than others, but you can make lots of them. Cocoa butter is the same way. In the same way you can make a stack of baseballs (and make a sugar crystal), you can make stacks of baseball bats (and make cocoa butter crystals).
That building of the bat stack is called crystallization. Breathe. Keep reading.
It's just building a stack of bats - sort of like tinker toys. If you build it right, it will be strong and stable. And you will have 'tempered' the stack of bats.
What happens if you mess up and it falls over or shifts? Is the entire stack ruined? Do you have to throw it away? Nope. Sure, the 'stack' is ruined (the temper) but the bats are fine. You just have to unstack it (melt the cocoa butter (chocolate)) and restack it. And you can do it over, and over, and over (as long as you don't set the bats of fire - or burn your chocolate).
Can you see that? I hope so. That's it. Really.
Now, on a similar note, and analogy, people want to know why each chocolate tempers a little differently.
Well, chocolate is not just a stack of bats (cocoa butter). Cocoa butter, first off, is not just one size of bat. Some of the bats are shorter. Some are longer. Some are a little thicker. Some a little thinner. Go figure. Not fair. Real life. Next, you are not just dealing with bats (cocoa butter). You are tempering chocolate and chocolate has sugar (baseballs). And not all the baseballs are the same size. Some are softballs. Some are tennis balls.
Oh, and heck, there is cocoa in there too. It's not all pretty and even like sugar or cocoa butter. Rock. Gravel. Same rough size, but not pretty (but it is tasty). And one origin may have pea gravel, and another may have 3/4-, and yet another, pretty(ish) river rock.
And you have to make an stable, 'pretty', strong stack of bats, balls, rock, gravel and stones. And you wonder why there is no one perfect, exact, 100% consistent, fool-proof way to temper chocolate? It's obvious isn't it that every stack of bats and balls and rock will be a bit different? That's it. From 100 feet away (out of the molecular level), it looks the same...BUT....IT....IS....NOT. And because it is not the same, you can not use the exact same method to stack every stack.
And so you have to follow this general method of tempering, where you can't really see what is going on, and you don't know what you are starting with (long bats, short bats, river rock?) but if you follow it, most of the time it will work. Some times your ball and bat sculpture will fall over, or really just shift, so lots of bats are showing, and your chocolate blooms. But now you know it's just a stack of balls and bats and rocks and sticks that you can take apart (melt) and put back together (temper) again.
Happy building.