Tint Lock Serum is a multi-tasking brow serum that works to condition hairs and help your eyebrow tint last longer. Why you'll love it Our Tint Lock Serum is infused with a powerful cuticle interlock system that works alongside the amino acid action to repair, rebuild and strengthen hair structure. It also harnesses an invisible, flexible film, that lightly coats the brow hairs to help hold in colour. This makes it an ideal serum to care for brows after treatments, if you have brittle, damaged brows, or if you find tint fades quickly and want to prolong the intensity.