PA-31 Navajo/Chieftan/Mojave/T1040
Air Traffic Control Fully Certified
Air Traffic Control Time Certified In Pos 1 (yrs) 3
Time Pressure
Conflict NMAC
Air Traffic Control Separated Traffic
Procedure; Airspace Structure; Human Factors
Working light traffic.  Had just taken over the sector.  Aircraft X was southwest-bound at 8;500 headed to NYC area.  I observed a 1200 target moving in the same direction approximately 7 miles south of Aircraft X's position.  As they were headed in the same direction; no potential conflict appeared to exist; and I took no action.  I then observed the 1200 target make a sharp right turn; placing the target in conflict with Aircraft X. I issued the traffic to Aircraft X as 'just turned northwest; 8;500 feet about 10 seconds later; I determined the two targets were on a collision course and said 'Traffic Alert; Aircraft X climb 500 feet immediately.'  I chose a climb because I would expect the other aircraft to dive if he saw Aircraft X; and a turn would not be sufficient given proximity to separate the targets.  I observed Aircraft X comply with the instruction; and reported the aircraft in sight as I observed Aircraft X at 8;700. I observed the 1200 code aircraft at 8;600; and the targets merged with Aircraft X indicating 8;900. Aircraft X reported the other aircraft to be a Lancair.This happened because the 1200 code aircraft did not see Aircraft X.  Fortunately; I saw the conflict in time to take action to separate the aircraft.  This was a very close call.We need to reach out to local pilot groups and encourage them to get flight following.  If I had been talking to the 1200 code aircraft; I could have taken action much sooner to prevent these aircraft from getting so close to each other.
Boston Center Controller reported a Near Mid Air Conflict between a VFR aircraft under Center's control and a VFR aircraft not under ATC control.