Strathclyde Police have said they were not ruling out terrorist activity as the cause of Wednesday's explosion in a woods near Loch Lomond.
A large area of Priory Wood near Gartocharn has been cordoned off, as police continue their investigation.
Explosives experts and forensics teams are poring over every inch of the woodland clearing.
Police said the fingertip search was going to be painstaking and time consuming.
Officers are investigating damage to trees in the woodland area about 300 to 400 yards from Ross Priory, a 19th century function venue owned by Strathclyde University.
The latest briefing from Strathclyde Police, which is leading the investigation, said a number of specialist officers were currently searching the scene.
This team includes officers from the Metropolitan Police and scientific and Explosive Ordnance Disposal (EOD) trained personnel.
The force said the level of detailed search required was likely to "take some considerable time".
Speaking near the entrance road to Ross Priory on Friday, Ch Supt Calum Murray said police expected to be at the scene for "a while yet".
Asked whether the inquiry was related to terrorism, he said: "As I said yesterday, we haven't ruled out any line of inquiry.
"We need to find out what happened. We are using the experts to assist us to do that."
He added: "I know a lot of time has passed, but these things take time. Today we are in the course of beginning a painstaking fingertip search.
"That is a significant undertaking. That will take a while."
He said: "Broadly you are dealing with an area of woodland in which felling has been taking place and there's wooding operations.
"Clearly we've got a centre of operations that we are focusing on and what we need now, having identified the area we are interested in, is to make sure the entire area is safe.
"We want to reassure the public there is no ongoing or residual threat to them, we have the matters very much under control."