I've found links here and here on making finishing salts, but this isn't the kind I'm talking about.  These are just mixtures of salt and some flavoring.  I'm referring to salts like Maldon Sea Salt and Fleur de Sel.  I know that these have (purportedly) minerals that make the salt taste richer.  Back when I was working in a kitchen, I was taught that part of what makes these nicer is that they're large crystals that dissolve slowly on the tongue (instead of nearly-instantly like your run-of-the-mill Morton's).  So basically, I want to try making my own large salt crystal flakes.  Maybe I'll use kosher salt instead of iodized salt, but the goal is to get large crystals that look like this, or even larger.  Finally, the questions:   Has anyone done this before?   What should I keep in mind? What should I look out for? How can I maximize crystal size? Is there any overlap with growing crystals in general?  
  A simple way to get "more" out of your salt, is to start with BIG crystals, and coat them gently in oil before sprinkling them over the food. That way they do not melt on contact with the food as they are protected from the water by the film of oil , and add a awesome crunchy texture to the serving.     Technically I think that your question is more chemistry related and not directly cooking related.  I can give you a few hints no what you can do to get crystals, but a chemist should be able to give you a lot better advice.  First, making the salt water solution:   Get distilled or at least demineralized water. You do not want to add random minerals that are dissolved in water to your salt :) Make a saturated solution of salt-water at a high temperature ... something like 90-95C (~194-203F). The idea is that at higher temperatures you get more of the salt dissolved in the water more easily. Keep the salt solution at that high temperature (well covered to reduce evaporation) for some time to make sure that any undissolved salt has settled to the bottom. You are interested only in the salt in the solution. Take only the saltwater without any undissolved salt. Until and including this step, the solution should be best keep at the same temperature. If you have to move the solution, at least make sure that the thing that you are moving it into is not cold.   OK, now it is time to make the crystals:   Crystals grow. If they grow too fast or are disturbed (thermally or mechanically) they fall apart and end up being smaller. This is why when you make ice cream you churn the ice constantly (mechanical disturbing the formation of possibly ice crystals) or chill it with liquid nitrogen (thermally shocking the crystals and make them break apart). What you get are very small crystals if you disturb them. Crystals grow when they are "forced out of solution" - that is, when the concentration of the salt in water is higher than the solubility of salt in water at that specific conditions. Pressure is one of the factors, but we will just ignore it completely. The factors that you can work with are Temperature and concentration (just remove water from the solution by evaporation) To get BIG crystals, you have to let them grow slowly. So, what you need to do is to cool the solution very slowly AND/OR Evaporate the water out of solution very slowly (take care not to     get dust in the solution during this procedure :) )   Unfortunately this is all the advice that I can give you now. Be aware that crystals are delicate and you might need a few attempts until you get the desired result. As a fun fact, there exist conditions where you will actually get a BIG salt Cube aka, a single salt Crystal by doing this :) . Cool indeed , but not very useful for cooking :) 