Layout Fluid

Basics

• A (Typically Blue) Semi-Transparent Lacquer of sorts used mainly in Machining for Helping in Layout / Marking Out of raw material/rough parts for further machining steps
• A Similar Tool is a Carpenter's Pencil / Grease Pencil
• You can scratch/scry off this thin layer with a Compass etc without effecting the Surface Finish of the metal below

External Links

• The Wikipedia Page on "Marking Blue" AKA Layout Fluid
• A Video by the YouTube Channel "Adam Savage’s Tested" Titled "Adam Savage's Favorite Tools: Machinist's Blue Layout Fluid" ( ~11 Minute Watch )