marking blue
{{short description|Layout stain used in metalworking}}
{{distinguish|engineer's blue}}
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file:Engineers Blue Naomi SexyCyborg Wu 2019.png
Marking blue or layout stain (sometimes called Dykem after trademark erosion of a popular brand, or Prussian blue after the blue pigment) is a dye used in metalworking to aid in marking out rough parts for further machining. It is used to stain or paint a metal object with a very thin layer of dye that can be scratched off using a scriber or other sharp instrument to reveal a bright, yet very narrow line in the metal underneath.
Composition
Marking blue is made by mixing methylated spirits with shellac and gentian violet.{{Citation | last = Brink | first = C. | last2 = McNamara | first2 = B. | title = Engineering Fabrication & Boilermaking | page = 44 | publisher = Pearson South Africa | year = 2008 | url = https://books.google.com/books?id=coOZXYLqqPoC&lpg=PA44 | isbn = 978-1-77025-374-2}}.
Alternatives
A felt tip marker can be used as they are convenient and tend not to dry up as quickly. On rough structures, such as castings or forgings, whitewash or a mixture of chalk and water can be used. A solution of copper sulfate, distilled water, and a few drops of sulfuric acid can be used on machined surfaces.
References
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