There are two basic products. Engineers blue in a tin is a sticky paste used to identify high points when scraping. For instance if one wants to scrape a surface flat against a reference (surface plate) the work is smeared with a thin layer of engineers blue. The work is then pushed across the reference surface. The points where the blue has been rubbed away are high points and need to be scraped. Then repeat as required. The watery blue liquid in a bottle is for marking out. It's painted or wiped on where it dries and leaves a thin blue sheen. Scribed line then show up more clearly.

Andrew

I use both Jon

For quick jobs, then a black 'Sharpie' works well on both steel and brass. It's convenient and quick – so a quick dab on a turned part to mark (say) the length of cut – is very handy. It does rub off fairly easily though, so it's not quite as "permanent" as the name suggests – at least on metal.

For larger/more involved work I still use Marking Out Blue – my small bottle of which I purchased from GLR donkeys years ago. You just paint it on with a small paint brush (I use children's ones). After use just let them dry out – they will soften very quickly when re-dipped in the blue. This blue stays on a lot better than Sharpies but can still get worn/rubbed away as the work progresses. So quite often I will place a few punch marks on marked lines for instance to keep the important reference points even if the marking wears off.

Many here will just drill/cut straight from DRO readings these days of course but I still like to see parts marked out.

Regards,

IanT

If you mark out you get a chance to think about whether it’s right before you cut metal. If you are confident then a DRO and diving straight in is a quick way to work but a mistake can be more difficult to rectify than rescribing a line.

Mike

Clean the oil off

Please forgive the slight digression, but I must mention a recent ‘find’

I was reading a piece about making steel clock-hands, in which it was casually mentioned that the material was ‘blued’ prior to marking-out with a very fine scriber.

“Nothing unexpected in that“ you might say : but the author was talking about blueing with heat [as one would normally do when finishing the hand]

This seems an exceptionally good idea, if the workpiece is suitable.

MichaelG.

Scraping is the classic application of Engineering Blue paste but it's good for identifying any area of poor fit, like checking tapers, or confirming a gib is pressing evenly. A small tin lasts forever.

It's possible to make a 3rd rate layout blue substitute from paste by dissolving it in Meths. Inferior to real Layout fluid and felt-tip, but handy in a pinch.

Before layout blue, steel was dipped in slightly acidified Copper Sulphate solution, which deposits a thin layer of Copper on the surface. Works quite well, but fussy. Dipping tanks take up space and the chemicals are a mild hazard. Mostly I use felt tips. Decent brands work better than pound shop cheapies, but it's not critical

All layout fluids need a clean surface – remove oil first.

Dave

Edited By SillyOldDuffer on 17/09/2020 09:56:08

I don't have that many projects on the go, mainly small engines, & then only one at a time; I prefer to use Jumbo markers for any flat surfaces & chisel pointed sharpies on others so find them quite effective.

During my apprenticeship we were taught to use Dyekem layout fluid as the preferred method but we also used copper sulphate mix, whitewash mix ( white lead ) on cast srfaces, now long since banned. I belive Copper Sulphate is still obtainable from some gardening centres if you want to try that out. To date; jumbo & Sharpies do fine for me.

George.

Jon,

You mentioned "cold blue". This is totally different. it is used to produce the protective bluing of steel used on guns etc. While you could mark out through tthis I won't help with your problem because it won't work on oily material. And of course it only works on ferrous metals.

Robert G8RPI

Edited By Robert Atkinson 2 on 17/09/2020 12:11:34

Prussian blue (Mine is Micrometer Brand &nbsp is DIFFICULT to remove from fingers, but ideal for scraping surfaces.

For marking out, Spirit blue is the one to use. Again hard to remove from fingers!

A Sharpie or a blue felt tip (Chisel point) can be used for marking out, but, is not as durable, in my experience, as spirit blue.

HTH

Howard