The invention relates to an accelerator solution comprising a complexing agent selected from the group consisting of complexing agents having a nitrogen atom and a hydroxyl group and bipyridine, a salt of a metal selected from the group consisting of transition metal, magnesium, and lithium, and optionally a solvent, wherein when the complexing agent has a nitrogen atom and a hydroxyl group, the amount of complexing agent in the accelerator solution is at least 5 wt %, based on the total weight of the accelerator solution, the amount of solvent is less than 50 wt %, and the amount of diethylene glycol as solvent is less than 25 wt %, based on the total weight of the accelerator solution.