Are you going to find reference materials about grinding salt for salt bars, probably not. Why would you not believe us whom have made hundreds of salt bars that it can happen. I have had it happen when I was first learning. Because you have not experienced it yet does not mean it will not happen, are you really willing to risk it over some silly salt when you can use a different kind of salt. Nope, not me. In manufacturing many times experience means much more than what is written down. I will not even sell some I have that turned out prickly just using a different brand of fine sea salt. You do not want to believe us then keep grinding your salt and one day you may wish you had not. Why are your bars stinging your skin? I you using them on broken out skin or are your salt bars leaving minute lacerations that are stinging? As for any benefits from using different salts in salt bars you are talking something that is on the skin for a few seconds and washed off so even table salt makes a nice salt bar. Many here use canning salt which also works. Grey Sea Salt and Himalayan Salt even in fine grain tend to be scratchy. Also it is not at all advisable to use med to large grain salt on the top of a bar for decoration, even if it does look nice. It can be hard to remove off the bar and customers very possibly will not think to remove it. If you want Mediterranean Sea salt then purchase fine. It is cheap and much safer, although I have never used it as the only salt only in a mix and really do not know if it will be prickly. I normally mix Pacific Sea Salt with non-iodized table salt. You have 2 choices here, learn from us that have been making salt bars for years or learn the hard way...I've just recently become a member here and saw your comments the first day about how lacerations can occur to the skin if ground salts are used in one's salt bars. I've been grinding Mediterranean Sea Salt to a powder and adding it to my FL HP salt bar batter, and I've been using those finished bars sometimes with washcloth application, sometimes directly on my face. Not once have I noticed lacerations. I will admit though, that repeated soap-ups at delicate skin locations during an extended tub bath has caused a slight sting, but that goes away upon thorough rinsing. I'm 70 years old and, as is common to us in later years, my skin has become thin. My husband tested the salt bars, too, as has someone else who bravely tests new batches for me. I've asked about whether or not they've experienced lacerations, stings, burns, or itchiness. So far, nobody has.
Because I have customers who are very interested in buying salt bars after I age them for an extended period of time, what I read in your comments has caused me great concern. Therefore, I've researched hundreds of pages in cyberspace, gone through all of my books, viewed many journals / papers, and aside from seeing the obvious testimonials / comments / complaints about skin lacerations / irritations brought about by using soaps made with coarsely ground salts that didn't dissolve in the bar as well as left on top of the bars as decoration, I can't find anything about finely ground and/or powdered salts being like chards in salt bar soaps that can and do lacerate the skin.
I do have the utmost respect for all of you experienced soap makers, and respectfully request that you assist me in my research by providing any reference materials that confirm how grinding salt can and will cause sharp shards to remain in the soap. I by no means am presenting a challenge to your expertise and years of experience... I just want to make sure that the salt bars I create using powdered Mediterranean Sea Salt carry very little risk of harming anyone's precious skin and I thank you in advance for any reference material you can suggest for me to look at.
https://www.sfsalt.com/inc/sdetail/mediterranean-sea-salt-fine-grain---5-lb--bulk-bag/701756#/submit