@TexChik I used to use a black seed ointment on my feet at night, put a plastic bag over each foot and a pair of light socks and sleep with that on all night for about 3 nights in a row. It would dissolve any calluses built up on the bottom of my feet, some so bad they were starting to crack at the heels. I was selling black seed products and my friend said her nieces were doing this and it was quick. I only had to do it a few times and maybe once a winter after that. Also found taking beta carotene supplements helped with the callouses building up for some reason.
