Marking blue
A blue dye for marking metal in machining and layout work
No single value: Marking blue is a material, and its colour varies. The background shows its family, blue.
Marking blue is a blue dye applied to metal surfaces in workshops to help mark precise lines for machining. It is made by mixing methylated spirits, shellac, and gentian violet, and is scratched off to reveal clear marks on metal parts. The name 'Dykem' comes from a well-known brand, and it is sometimes called Prussian blue after the pigment.
- Used to mark precise lines on metal before machining
- Made from methylated spirits, shellac, and gentian violet
- Also called layout stain or Dykem
- Scratched off to reveal bright, narrow lines
- Alternatives include felt tip markers and chalk
What colour is Marking blue?
Marking blue is a blue liquid dye used in metalworking, especially for marking out lines on metal parts before machining. When brushed or painted on, it forms a thin, coloured layer that can be easily scratched away with a sharp tool, revealing a bright line against the metal. This makes it easier for machinists to see and follow precise markings during cutting or shaping. It stands out from other marking methods by providing a clear, narrow line that does not smudge easily.
Where does Marking blue come from?
The term 'marking blue' describes its use and colour, while 'layout stain' refers to its role in marking out work. The name 'Dykem' became common after a popular brand, and 'Prussian blue' is sometimes used due to the similar pigment. The product is not tied to a particular country or region, and its use is widespread in metalworking industries.
How is Marking blue made?
Marking blue is prepared by combining methylated spirits (a type of alcohol), shellac (a natural resin), and gentian violet (a synthetic dye). This mixture creates a thin, quick-drying liquid that adheres well to metal surfaces. The dye is applied in a light coat and dries to a visible blue film, which can be scratched away cleanly to show the metal underneath.
Where Marking blue is used
This dye is mainly used in metal workshops and factories. It helps machinists and metalworkers mark out lines for cutting, drilling, or shaping metal parts. The clear, bright lines made by scratching through the blue layer are easy to see and follow. Alternatives include felt tip markers, whitewash, or chalk mixtures, but marking blue is valued for its precision and clarity.
Blue around the world
What the blue family means from country to country.
Lapis lazuli has been mined in the mountains of Badakhshan for more than six thousand years. Ground to powder it gave ultramarine, the costliest blue in European painting.
Royalty and powerSacred and holyAweSource: Lapis lazuliThe chadari is a full-length covering for women with a mesh panel over the eyes. In Kabul and the north it is most often a light blue.
Protection and healingSource: BurqaThe blue band of the flag stands for the wish of the Armenian people to live under peaceful skies. The red above it is for the highlands and the struggle to survive.
Politics and protestHopeSource: Flag of ArmeniaThe flag is sky blue, white and sky blue, created by Manuel Belgrano in 1812. National teams are called the Albiceleste, the white and sky blue.
Politics and protestPrideSource: Flag of ArgentinaBoca Juniors play in blue and gold. The club's story is that in 1907 it took the colours of the flag of the next ship into port, which was Swedish.
Festival and celebrationPrideSource: Boca JuniorsTo be true blue is to be honestly and loyally Australian. The phrase is older than the country, but Australians have made it their own.
Politics and protestTrustSource: True Blue (John Williamson song)Shades and relatives of Marking blue
Marking blue is sometimes confused with Prussian blue, a pigment, but they are different materials. Other marking methods include felt tip pens, whitewash, and copper sulfate solutions, each suited to different surfaces or needs. The main difference is in the clarity and permanence of the marking.
Questions people ask about Marking blue
What colour is marking blue?
Marking blue is a blue dye that forms a thin, visible layer on metal surfaces, making it easy to see where lines are marked out.
What is marking blue made from?
It is made by mixing methylated spirits, shellac, and gentian violet, creating a quick-drying blue liquid for marking metal.
Why is it called Dykem or Prussian blue?
Dykem is a common brand name that became widely used for marking blue. Prussian blue refers to the similar blue pigment, though the two are not the same.
How is marking blue used?
It is brushed or painted onto metal, then scratched with a sharp tool to make clear, bright lines for machining or layout work.
Good reading and sources
The facts on this page come from the Wikipedia article "Marking blue", written by its contributors and used under the CC BY-SA 4.0 licence, and from its Wikidata record (CC0). Rang rewrote the text in its own words, with AI assistance, and compares every page with the article to make sure no passage is copied. It may be reused under the same CC BY-SA 4.0 licence with a link back.
It may contain mistakes. The swatch is an approximation: named colours are not fixed standards, and every screen shows them a little differently. If something is wrong, tell us. Last refreshed 2026-10-03.
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