Soft iron knot?

[A440A@AOL.COM]

Greetings, 
    Having recently been the tech on a four day historical recording project, 
I had about   as much trouble as I ever had getting a clear sound out of a 
fortepiano.  We were using a copy of a Graf, and I was tuning a Young 
temperament for a Schubert CD.   Aside from the continual action abberations, 
I had a couple of broken strings. 
   I tried tying the broken strings, I used two different knots that have 
worked for me for many years, and neither string could be brought near its 
pitch without breaking at the knot.  
   Is there a particular type of knot that is known to work with soft iron 
strings?  These were Rose, .080" wires.  
Regards, 
Ed Foote RPT