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To try to get a grip on GWR Locomotive green in model form I bought a cheap colorimeter:

215711740_IMG_20200924_133452r.jpg.b8563ea1c88dcd35a85381370c0b75b5.jpg1333107226_IMG_20200924_133715r.jpg.8268a2de150b68c8a73672dd61c48a30.jpg1345169858_IMG_20200924_133808r.jpg.1e6c02f0d77bcadab500f4cd65398fcf.jpg

 

This device measures colours using it's own calibrated light source and gives results in a colour space called CIELAB, which is device independent and is widely used to specify and compare colours throughout manufacturing industry.

 

CIELAB (more correctly "CIE L*a*b*") is an international standard that describes colours in absolute, unambiguous mathematical terms. The three components of CIELAB are:

  • L*: lightness 0 to 100
  • a*: green to red (usually given in the range -128 to +128)
  • b*: blue to yellow (usually given in the range -128 to +128)

 

By changing the values of each of those three components you can specify every colour that the human eye can see. Each colour can be thought of as a point within a 3 dimensional shape - a cylinder with the L value measuring the height of the colour within the cylinder.

At the bottom of the cylinder where L (lightness) is 0, colours look something like this:

1042879884_CIELAB0.png.3d80b8c7fe0beb45b8ad3a74d9e893cb.png

 

At the top, L lightness is 100:

153139530_CIELAB100.png.6d43a11a650fce35e7f7752827211dbe.png

 

 

In the middle, around where GWR Loco greens are found, it looks like this:

707798641_CIELAB30.png.959dd48e00fc3cc0bb4858b9120a9868.png

 

To be able to compare CIELAB measurements against each other, and to reproduce them accurately, it's important to know the colour of the light source that was used to measure them. My new device uses a standard D65 illuminant with a 10° field of view, which is equivalent to noon daylight.

 

So, the colorimeter should give objective measurements of loco colours without any bias due to the perception of the viewer or the lighting conditions. I just need to be able to get access to a flat area of colour at least 8mm diameter on the models I want to measure.

 

More to follow...

 

Edited by Harlequin
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Does it have a white and black tile to calibrate it before use?

 

Probably not particularly reliable if not, unless technology has come on in the last few years. 

 

If you've got one loco that you're happy with, you could set that as your standard, and measure all others against it.

 

Are you glossing the surface up first? If not, it'll affect your ability to compare other locos of a different gloss level.

 

(Colourist in the plastics industry from 1993-2005.....)

 

 

 

 

 

 

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I'm interested in the concept of 'scale colour' - how the perceived colour of a model changes depending on at what distance the model is viewed. The further you get from a painted object, the lighter the colour appears?

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Hi Tim,

3 hours ago, Tim Hall said:

Does it have a white and black tile to calibrate it before use?

The device runs a series of self-checks when it starts up including an "internal whiteboard" test. The operating instructions do not suggest any kind of external calibration is needed, or even possible.

 

The acid test will be whether it gives the same reading for a known sample colour (or colours) over a long period of time.

 

3 hours ago, Tim Hall said:

 

If you've got one loco that you're happy with, you could set that as your standard, and measure all others against it.

Yes, that's a possibility which might help me but other readers might want to use a different loco as their personal baseline so I'm not sure that publishing results in that form would be generally useful.

And of course, we know that GWR Loco green varied over time, even during the first weeks after out-shopping due to effects of heat on the varnish, so there is not one single loco colour that I'm happy with. I expect them to be different.

 

3 hours ago, Tim Hall said:

 

Are you glossing the surface up first? If not, it'll affect your ability to compare other locos of a different gloss level.

 

(Colourist in the plastics industry from 1993-2005.....)

 

I won't be glossing up the surfaces. Model loco paint finishes are generally very similar in terms of the gloss level and I will rely on that to allow model colours to be compared. I also don't want to add another variable in to the measurements which might complicate things and make it more difficult for others to reproduce my results.

 

In theory anyone who cares to buy one of these colorimeters should be able to measure the same make and model of loco as me and get the same results, within some acceptable level of tolerance.

 

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3 hours ago, Paul H Vigor said:

I'm interested in the concept of 'scale colour' - how the perceived colour of a model changes depending on at what distance the model is viewed. The further you get from a painted object, the lighter the colour appears?

 

Hi Paul,

 

That's an interesting topic but I'm not going to get into it yet. It might eventually be possible to quantify the effects of scale and/or distance as a vector in CIELAB space but first things first - I need to just get some basic colour readings and see if they say anything about the relative colours of different locos.

(Yes, Hornby King class, I'm looking at you!)

 

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13 minutes ago, Harlequin said:

Hi Tim,

The device runs a series of self-checks when it starts up including an "internal whiteboard" test. The operating instructions do not suggest any kind of external calibration is needed, or even possible.

 

The acid test will be whether it gives the same reading for a known sample colour (or colours) over a long period of time.

 

Yes, that's a possibility which might help me but other readers might want to use a different loco as their personal baseline so I'm not sure that publishing results in that form would be generally useful.

And of course, we know that GWR Loco green varied over time, even during the first weeks after out-shopping due to effects of heat on the varnish, so there is not one single loco colour that I'm happy with. I expect them to be different.

 

I won't be glossing up the surfaces. Model loco paint finishes are generally very similar in terms of the gloss level and I will rely on that to allow model colours to be compared. I also don't want to add another variable in to the measurements which might complicate things and make it more difficult for others to reproduce my results.

 

In theory anyone who cares to buy one of these colorimeters should be able to measure the same make and model of loco as me and get the same results, within some acceptable level of tolerance.

 

Hi Phil

 

In an early edition of Backtrack David Jenkinson wrote an article on locomotive colours. In the article was an anecdote  from a conversation he had with one of the chaps who mixed the paint for the GWR. It went along the lines of "If the night before was a good one and I came into work happy the ingredients were carefully measured and mixed. If she nagged me as I left the house they were just thrown in". 

 

Does you little machine have a paint mixer's wife "good night and a bad morning"  switch?

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I know  Bob Dance the Team Lotus chief mechanic for years  way back when what the actual colour of green they used .He gazed blankly and said we just went to he local paint dealer and asked for British racing green and thats what he gave us  ,Oh well . I also asked him him about the switch from a red colour instrument panel to black .Was it significant ? No he said .We ran out of red ..He also told me about Classic Team Lotus  matching the red Gold Leaf colour .He also told me of Chapmans naughty cheaty bits .Bloody lethal .The guy who painted the originals couldnt remember what paint he used .They traced it to a Volvo truck colour that wasnt used when the team originally used red.,When Classic were  matching up matt and semi matt black on suspension parts on later cars they came up with over 80 variations of matt black .

Jordan sent me their colour process for the  2002 fluro yellow  after I had signed a confidentiality  note .It was a salmon pinkish primer ,followed by fluro yello followed by an orange  tinted clear laquer. Jaguar cars  first season F1 colour cost 600 quid a litre  as did Simteks .When I met the guy at Brands who now races a Simtek i didnt have any paint left but did have the mix  list  him so he can replicate it .He was over the moon as no one could match it .It had about a dozen different tints  to it .The black  colour  on a Simtek was a very dark pearl blue.When you looked at it in a certain light it felt you you could dive in forever.i list all this stuff to show nothing is what  it seems paintwise .Its all bollox.I just paint my models to look good .Always have  .

Edited by friscopete
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1 hour ago, Clive Mortimore said:

Hi Phil

 

In an early edition of Backtrack David Jenkinson wrote an article on locomotive colours. In the article was an anecdote  from a conversation he had with one of the chaps who mixed the paint for the GWR. It went along the lines of "If the night before was a good one and I came into work happy the ingredients were carefully measured and mixed. If she nagged me as I left the house they were just thrown in". 

 

Does you little machine have a paint mixer's wife "good night and a bad morning"  switch?

It's the same with GWR station colours.  I understand that the painters were given a tin of maroon brown and a tin of white. Used neat for the chocolate and white bits. Add a bit of white to the Brown to make dark stone. Add a bit more white to make light stone. So again, variations were legion. Each station would have been slightly different to a greater or lesser degree.

Ian

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35 minutes ago, friscopete said:

The black colour on a Simtek was a very dark pearl blue. When you looked at it in a certain light it felt you you could dive in forever.

 

The perception of depth is the basis of the term 'lake'. A cheap undercolour (typically a dark red or brown oxide) followed by layers of varnish, which gives the impression of luxury and opulence. The Edwardians exploited this characteristic very well.

 

Lakes are unfashionable nowadays for modern railway rolling stock. Putting varnish over acrylics usually makes them look worse.

 

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At the moment I'm not intending to compare model colours to prototypes, just to compare them to each other in a quantifiable way for now.

 

However... I have got a copy of Railway Archive No.5, as recommended in Great Western Way 2nd Edition, for the article "Painting Victorian Trains" by Dr. Anthony J. East. It gives some useful clues about the formulation of GWR Loco green ("Middle Chrome Green").

 

The exact mix of pigments and the resulting colour was quite closely specified by Swindon and the GWR were very careful about their "brand identity" so I think colours would have been rejected if they were not up to scratch. We know about the effects of weathering and heating and we know some of the reasons why paint formulations and painting methods changed over the years. So, I think we can explain most variations without resorting to stories from the pub about chucking ingredients recklessly into the pot!

 

On the subject of Lakes, Dr. East says that lakes are a specific subdivision of organic pigments: "A lake is a chemical complex formed between a [soluble] dye [snip] and a metal salt. Together they react to form a stable insoluble chemical complex." "In general, lakes are darker and more violet than the dye itself."

 

He says, Alizarin, the natural dye extracted from the madder plant combined with an Aluminium salt creates Crimson Lake. Crimson Lake is transparent and so needs all those undercolours but I don't know if that's true of all lakes.

 

Edited by Harlequin
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A book just published, written by an employee at Swindon Works, joined after school and left when the Works closed,  he was an Apprentice in the Paintshop  and rose up through the Paintshop grades from the lowest grade and qualified a a Signwriter (top grade). The old hands showed  him all the fiddles.

Crackering was one fiddle of note, crackering is  white spirit added to the kettle of paint eg Rail Blue, makes the paint easy and fast to apply,  but ruins the gloss of the finish.  if you were caught crackering  paint , you were in trouble.  A useful anecdote which debases the obsession we modellers have with the "purity" of the  colours of our models.

 

 

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6 hours ago, Pandora said:

A book just published, written by an employee at Swindon Works, joined after school and left when the Works closed,  he was an Apprentice in the Paintshop  and rose up through the Paintshop grades from the lowest grade and qualified a a Signwriter (top grade). The old hands showed  him all the fiddles.

Crackering was one fiddle of note, crackering is  white spirit added to the kettle of paint eg Rail Blue, makes the paint easy and fast to apply,  but ruins the gloss of the finish.  if you were caught crackering  paint , you were in trouble.  A useful anecdote which debases the obsession we modellers have with the "purity" of the  colours of our models.

 

 

I think that's a story from BR days.

 

 

In Great Western days, the era this sub-forum is about, paints did not arrive in a ready made colour and did not naturally have a gloss finish. Thinners were a normal part of the paint formulation and in fact white spirit was the specified thinner for the "China Red" used on buffer beams.

 

To re-iterate, I'm not suggesting there is any one "pure" colour for GWR Loco green.

 

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After trying a few measurements I realise that getting meaningful results is going to be more involved than I thought!

 

1. If I repeat measurements in roughly the same spot I get slightly different results every time. Fair enough but that means that I will need to take a number of measurements and average them out before it's safe to post any numbers here.

 

2. The colorimeter can tell you whether two samples are close to each other within a defined tolerance. When I sample one side tank of my Hornby 6110 Large Prairie all the samples are fine, within the tolerance but here's the kicker... When I compare that colour with the other side tank it's consistently outside the tolerance and the colorimeter reports a colour match "failure"! The biggest difference is always in the L axis - in other words one side is darker than the other... I suspect the paint has not been sprayed evenly on both sides.

 

That's an interesting finding already, even if it does make my idea of comparing models much more difficult.

 

3. When I try to convert the CIELAB values into colours that my computer can display (on a properly calibrated monitor) the results are always more grey than green - green-ness is barely detectable. I don't know yet if the conversion is going wrong, my monitor is wrong, my eyes are wrong or the colorimeter is wrong.

 

So I have some problems to work through here!

 

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11 hours ago, ikcdab said:

It's the same with GWR station colours.  I understand that the painters were given a tin of maroon brown and a tin of white. Used neat for the chocolate and white bits. Add a bit of white to the Brown to make dark stone. Add a bit more white to make light stone. So again, variations were legion. Each station would have been slightly different to a greater or lesser degree.

It wasn't just a variation in the colours as mixed (which would, of course, vary in perception even more as they weathered over time) but that the precise areas to which those various colours were applied varied according to which painting team (or foreman?) did the job. Despite apparently precise specification, careful study of individual locations over time has shown that, if the specification could be interpreted in more than one way, it was, with repainted structures often having slightly different applications of the specified colours to those that had been there prior to repainting. Sometimes this was no more than a colour change starting at, say, the seventh plank up rather than the sixth, sometimes it was a little more drastic.

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I have posted this before but many years ago I visited WIilliamsons paint factory in Ripon, on the wall in the reception were no less than over a dozen different green which were different "accurate" GW Greens they had been asked to mix for preservation groups. Apparently they made one to the satisfaction of the first enquirer then second wanted it altered and so on.

 

There are a number of factors at play, the hand mixing of paints, the stability of the colouring substances used, how the paint ages, the effect of direct sun and the effects of pollutants in the air. It may be that  the only colour model wise that is wholly inaccurate is the strange bluish green Hornby have inflicted on a number of models.

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I have a  genuine BR era Swindon green painted object carefully stashed away out of daylight so can readily check the exact full size, non-scaled, colour from a part of an engine which did not get hot but did of course get dirty and weathered ;)

 

PS It doesn't match any WR green applied by Hornby (but note it is full size so not scaled down in any way).  Incidentally having scraped back several layers of paint applied to the edge of a cast iron numberplate offa 2251 I can confirm that the green definitely varied a bit, for whatever reason.

Edited by The Stationmaster
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36 minutes ago, The Stationmaster said:

I have a  genuine BR era Swindon green painted object carefully stashed away out of daylight so can readily check the exact full size, non-scaled, colour from a part of an engine which did not get hot but did of course get dirty and weathered ;)

 

PS It doesn't match any WR green applied by Hornby (but note it is full size so not scaled down in any way)

 

The only problem with that is that the objects the paint was applied to would be subject to daylight. Also there could be chemical decomposition within the paint sample altering it over time. My personal colour hang up is London Midland Region Maroon, it has to be as I remember it. For faded paintwork on buildings I use Humbrol wine (73). It’s nothing like maroon but looks right to me.

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My conclusion on this subject was reached many years ago, and I have never seen any reason to change it.  It is, if the model looks the right colour to you under the layout’s normal lighting, fine, don’t worry about it and get on with your life.  If not, repaint the model  until it looks ok, then don’t worry about it and get on with your life.  
 

There are too many variables to pin colour down, you need to calibrate all the equipment to an established standard, including nature and your eyes, allowing for how many sunspots there are at the time the colour was recorded, and now, and next time you look at the model.  Geological time is too short, never mind life!

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22 hours ago, ikcdab said:

It's the same with GWR station colours.  I understand that the painters were given a tin of maroon brown and a tin of white. Used neat for the chocolate and white bits. Add a bit of white to the Brown to make dark stone. Add a bit more white to make light stone. So again, variations were legion. Each station would have been slightly different to a greater or lesser degree.

Ian

Like Mr Hall I've done some time colour matching in the plastics industry and I find that tale impossible to believe. My experience suggests that if individual painters mixed colours the results would have been appalling with different parts of every station in radically different colours. In GWW it states that up until about 1920 the foreman  was required to mix paint against a standard colour chart, and after that the paint was supplied pre mixed from the manufacturers.

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22 hours ago, ikcdab said:

It's the same with GWR station colours.  I understand that the painters were given a tin of maroon brown and a tin of white. Used neat for the chocolate and white bits. Add a bit of white to the Brown to make dark stone. Add a bit more white to make light stone.

 

 

Where did that nugget of info come from? Seems at odds with the info that the GWR were buying in paint from outside suppliers from the early 1920s. It may have been mixed on-site in the early days, but the maroon brown they used didn't come in until the 1930s.

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9 hours ago, 57xx said:

 

Where did that nugget of info come from? Seems at odds with the info that the GWR were buying in paint from outside suppliers from the early 1920s. It may have been mixed on-site in the early days, but the maroon brown they used didn't come in until the 1930s.

Well I don't know it's one of those anecdotes I grew up with. More research required.

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12 hours ago, 57xx said:

 

Where did that nugget of info come from? Seems at odds with the info that the GWR were buying in paint from outside suppliers from the early 1920s. It may have been mixed on-site in the early days, but the maroon brown they used didn't come in until the 1930s.

GWR Signal Department painting instructions dating from 1907 refers to 'Torbay red' and 'white, Torbay'.  So at that time the Signal Dept, if no other, would seem to have been buying some in pre-mixed paints from a paint manufacturer (i.e. the Torbay Paint Co.)

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Worth persisting with this experiment IMO.

 

I had some paint ‘mixed to match’ At B&Q following measurement of the item I wanted to copy (a piece of artists mounting board). The device used to take the measurement looked very similar indeed to the one under  discussion here, and the resulting match is spookily good.

 

Having such a meter at home should facilitate ordering from a specialist paint supplier far from home ....... B&Q don’t sell the right sort of paint for model trains ‘mixed to match‘ to my knowledge.

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Always struck me the one opportunity that no model paint supplier has taken is to offer a range that matches RTR models with appropriate descriptions to a overcome brand issues like Blue Branch Line BR Green and Red Box LSWR 488 Green.

Edited by Butler Henderson
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No substantive updates yet but I have some more technology.

 

The website I was using to convert CIELAB values to RGB belongs to a company that makes another affordable colorimeter. (I didn't that realise until the wonder of cookies showed me adverts for their devices while I was looking at the weather forecast... :wink_mini:)

 

This device, a NIX Mini 2, is a very different beast:

1698333615_IMG_20200930_184305r.jpg.dbb9c98b4679768f1aa10380495e8ba3.jpg1770526225_IMG_20200930_184317r.jpg.28c15930fdc5952f5b3e51b2447102b5.jpg

 

The original blue device is far eastern basic technology - a standalone workmanlike unit. The new device is a slickly designed, tiny sensor module from Canada that pairs with a swish app running on a Smartphone.

 

1341832432_SAM_4486r.JPG.8bef6a680e8cbbd88e9d896a5510aae7.JPG

 

So I can now compare samples from the two devices and hopefully solve some of the problems with the initial measurements from the big blue device.

 

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