I just bought a 6-string nylon setThe top 3 strings (low pitched) are brass colored, the bottom 3 strings (higher pitched) are blackI string the brass ones just fine, but I have some trouble with the black stringsEvery time I string them and start to tighten them, they untighten and start to drop in pitch by themselvesNo matter how I string them, the same thing happensI'm a little frustrated right nowHow can I string them so they could be tuned normallyBecause every time I tune them, for example, one minute it sounds fine, then i check the same string 5 seconds later, and it's already flatWhat am I doing wrong?
