In my reading of older manuals and books, it appears that a red lead/oil mixture was used for marking/scraping up until (roughly) the mid 1930's, when the current prussian blue/grease mixture was adopted.
According to Wikipedia, Prussian Blue (the pigment)
*massively* predates the 1930's.BugBear (curious)
In article , bugbear writes
Don't know for sure but put forward two factors which may have been significant:
(1) Prussian blue has a very intense colour, probably visible in much lower amounts than red lead;
(2) Red lead (Pb3O4), like any lead-based pigment, is toxic, whereas prussian blue is not (despite being stuffed to the gills with cyanide ligands).
David
You've got me backwards; I wasn't asking why red lead was replaced, I was wondering why red lead held out for so long BEFORE being replaced...
BugBear
Don't remember using it for marking out and scraping , but I do remember using it for a lubricant on dead centers in the lathe. Some lathes had a little pot cast into the tail stock with a nib that fitted into the pot for the keeping of the red lead . A little dab on the dead center helped lubricate the centering hole.
Probably due to health concerns ,much like the omission of lead in paint products.
My apologies to Bugbear I inadvertantly sent a reply to his email address instead of this forum.
"does anyone know .. why it finally .. gave way to Prussian blue?".
David
Splendid piece of editing, altering my question substantially.
BugBear
No, I merely quoted the bit I was replying to, and removed the bits I wasn't. Maybe you didn't express your question as you might have wished.
David
Evidently.
*do* you have any idea why Prussian Blue didn't oust red lead sooner?BugBear
No, but I did on the other part of the question you asked (whether you meant to ask it or not), which is why I answered that and not the other.
Look, enough. I was trying to be helpful, if it upset you that is regrettable for you, get over it.
David
The artificial Prussian blue (PB) is a more intense colour than the natural red in red lead (RL). PB forms colloids and can be very finely ground. RL forms tiny platelets that resist reduction below a certain size. Thus, it is ideal in paint as they lie down overlapping one another as ther paint dries.
If you are scraping down a bearing, you will still be able to get high spots with PB that RL would not pick up. That's why it eventually won out over red lead.
Why not sooner? Partly cost. RL was easy to make whereas the process to manufacture PB made it relitively expensive right up until the First War.
I suspect that an innate conservatism in engineering helped to keep RL in use long after it would otherwise have vanished.
And if you look at the machinery around in that era (the only bearings I've seen scraped on something of importance from that era belonged to a Gypsy Major from a Tiger Moth) then it probably was of no consequence. I doubt that the precision required for (say) bearings for a heavy water enrichment centrifuge was called for....
Julian.
Ah - I had no information on cost-versus-time.
Especially if RL was "kicking around" the workshop for other purposes, which seems possible from the other posts.
BugBear
Ah, OK. I thought you'd simply misunderstood, which was the reason for my initial clarification.
BugBear
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