Alternative Engineer’s Blue — A DIY Solution
Some of you, especially some machinists, will find the title a bit ambiguous due to the use of “Engineer’s Blue”. Engineer’s Blue usually refers to the colored paste used when mating two components, however, it is sometimes also used to describe “Marking Blue” or “Dykem” (Named after a popular brand).
Now, what we’re taking a look at here is both! I’ll split the article into 3 parts:
- Prelude (You’re reading it now)
- Marking Blue (For marking, duh…)
- Engineer’s Blue (For scraping)
Marking Blue
This stuff is amazing!
Wikipedia describes Marking Blue as
… a dye used in metalworking to aid in marking out rough parts for further machining.
It is often refered to as “Dykem” and it, usually, has a blue color. However, some manufacturers also provide it in a red color.
To use it, you simply apply it to a surface and once it’s dried (It’s fast drying, usually within minutes) you’re free to “draw” your layout or markings using a scriber. The blue color creates a contrast to the scribed line, which will be the color of your materials surface. There’s not much more to it.
The color used in Marking Blue is traditionally Prussian Blue, however I’ve also seen Crystal/Gentian Violet used. I’m not entirely sure why one is preferred above the other, but I suspect that the fact Crystal Violet is a liquid and Prussian Blue is a pigment can have something to do with it. If the pigment isn’t of sufficient quality, it would need to be grounded/sheared (using something like a 3-roller mill) for it to be completely dissolved or dispersed. Atleast, this is true for making paint (and Marking Blue is essentially a dye).
Recipes
Some of the recipes that I’ve seen, and that I’d like to eventually test and write about, is listed below.
The most basic recipe
An alternative recipe would be
A more durable film can be applied using the following recipe. It will leave a thin copper film that is more resistant to rough handling.
- Copper Sulfate (Also known as bluestone)
- Distilled Water
- 2 drops Sulfuric Acid (Remember: Add acid to water, not the other way around)
For use on rough surfaces (Forged or cast metals)
- Chalk
- Water
Engineer’s Blue
Just like the Marking Blue above, this stuff is awesome!
When an accurately flat surface is needed a technique called scraping can be used. When scraping a surface, a reference surface is covered in Engineer’s Blue and subsequently mated to the subject surface. This will color the high spots of the subject surface which is then removed using a carbide or HSS scraper.
For this, the Engineer’s Blue has to be non-drying and easily transfer to the subject surface.
Recipes
The original patent for Dykem’s Hi Spot product is likely US2396667A as mentioned in this post. The recipe calls for:
- 1–3 pounds of oil soluble dye (It is mentioned, in the patent application, that Prussian Blue will damage the surface over time, and the actual ingredient is described as a “oil soluble dye” hints that another dye is used?)
- 30 pounds of petrolatum (In Denmark, primarily known as Vaseline)
- 1 pound of paraffin wax
Wikipedia mentions the following recipe, however one should keep in mind Adler Leon’s (The previously mentioned patent assignee) comment about Prussian Blue damaging the surface:
- Prussian Blue
- Grease
The US2396667A patent briefly mentions a recipe that seems to have been what was used prior to the patent.
Although the amounts of Prussian blue generally intermixed into the usual vegetable-derived (readily drying) carrier to make spotting paste, is nearly one-half of the bulk of the mixture itself…
One could imagine that the recipe would look like:
- 40% Prussian Blue
- 60% Vegetable Oil
Epilogue
I hope that the above recipes have inspired you. In the future, I hope to source as many of the above ingredients (I’m especially worried about Crystal Violet and Copper Sulfate as they might not be readily available in Denmark) and test them out.
