Linen drafting film

Up until 60 to 70 years ago important engineering drawings were usually done on linen drafting film (starched light linen cloth) since it is more robust than tracing paper. However it was replaced in the 1960s by polyester film.

Where I volunteer there are quite a few valuable drawings on linen film. These, most over 100 years old, are stored flat and in the dark. However the temperature and humidity varies considerably. My questions are:

1. How long can they be expected to last?
2. How does the film degrade?
3. How does one preserve the drawings?
4. What is the best way of copying them? Originally blue printing would have been used. Can they tolerate the later ammonia based copying processes? Obviously they can be photographed but flatness and light reflection could be a problem.

Any knowledgeable comments would be welcome.

JA

Where I worked the drawings were almost all on coated polyester film when I started there (up to A0). These were also photographed/scanned and positive 35mm film images were put into aperture cards for everyday viewing and printing. When networked computers became a normal desk top item the aperture cards were all scanned as tiff images available over the network. As CAD became the normal method of producing designs and drawings the images were saved directly to the network. By the time I retired I had three monitors on my desk. For some work I did I needed one for looking at drawings, one for a spreadsheet and one for the program I was working on to produce my work output. Without three monitors the paperless office was always going to be impossible.

I suspect the future will be all digital.

I still drew up full sized layouts on polyester film (using coloured marker pens) for pipe fabrications but getting the polyester film was getting harder by the time I retired. 1500mm wide film was the first to disappear.

Martin C

Edited By Martin Connelly on 18/04/2023 18:58:16

Depending on size, I would have thought a scanner would be the best option. A0 scanning services seem to be fairly commonly available if you have a few. If you have a very large number you might consider investing in a scanner.

Whilst unable to advise personally. I would suggest something like the V&A Museum or icon may be able to help. Links below:-

V&A

ICON

Edited By V8Eng on 18/04/2023 19:14:21

We had tracers who copied standard machine drawings onto linen using pens. When copying became available they were all transferred to aperture cards and microfilm. Copying was done by a local copy and print firm. No real use in keeping old fragile drawings, an easy way to copy is use a digital camera in daylight.

Scanning is an attractive option BUT make sure that someone keeps the media/format up to date. If you'd done it 40 years ago on 5"floppies you be a bit stuck, and the floppies themselves would have degraded.

At the Museum where I used to Volunteer we photographed our drawings both paper and linen with a poor mans studio and they came out well. The archive dept then catalogued them and they are now available for research. The originals are in a controlled capsule/room

I just overlapped the last of the tracer ladies, who had fine draughting skills and some of whom became draffies.

Ammonia printers! It must be hard to find somewhere to print the old continuous sheets, never mind A0 or double elephant. By the time I retired the customers all wanted prints at A3 so they could use their office printers.

Wide format scanners and printers are still common at graphics and printing companies. Peter aand Duncans comments on scanning are spot on.

Photography is a DIY option. Do it with the drawing vertical on a vacuum hold down box and LED strip lights. Use a digital SLR or similar camera with a good lens (I'd start with a 50mm prime lens). The vacuum box cam be a box (MDF or similar) with a face of perforated hardboard. This needs framing behind to keep it flat. Vacuum from a vacuum cleaner on low is enough to hold a sheet.

V8 comments on contacting the professionals on preservation is also spot on. That said linen and india ink are very durable materials. Mould is one risk.

Robert.

If photographing, there will be some distortion introduced (no lens is perfect). The distortion can potentially be corrected in image processing software (if it even matters for your end use).

This distortion was made clear to me when I tried to scan from 35mm film images of some engineering drawings. I used some raster to vector software to try to generate a usable CAD output, the results were unusable because every originally straight line on the original drawing had a slight curve on the film.

Up until the mid 2010s we were still having to dig out an occasional linen drawing from the 1950s and print it. It just went into the large copier and the original was hung back up in the cabinet again. Beautiful prints with very little distortion. The linen drawings even had those curious inch things on them!

Provided the linen original isn't really delicate it should copy in a large photocopier at pretty well spot on 1:1 or whatever size you want it; scanning at 1:1 should give good results but probably a huge file size.

As others have said, using photography (and therefore huge reduction in scale) introduces other problems, but it does mean that storage of the image is simplified. Provided you don't really need to use it, but just look at it and start wishing you still had the original, because that dimension in the corner is now illegible...

Some good suggestions above!

I remember we occasionally had to do changes some linen drawings, it was a nightmare especially if had already been modified. A lot of linen drawings were given to apprentices to trace and when they were signed off we used to wash the coating off in hot soapy water to make lovely soft dusters, anyone esle do that?

For the Robertson Clock at Bristol we used a commercial reprographics company that had a large format scanner. Store the images ideally in the cloud as well as on local mass media such as HD and/or DVDRom. If you have another cloud contract which includes auto backup that's a bonus. For example I use Google Drive for documents I want to keep and my local PC is backed up by Norton.

To answer JA's point regarding Ammonia, the drawings don't come into or any where near liquid Ammonia. UV Light passes through the drawing which is placed on top of a sensitised paper sheet, passed through a light chamber via rollers. The exposed paper is then fed through an Ammonia vapour chamber which 'Develops' the coating, the master being separated from the print before that operation. Yes Henry, we used the 'Dusters' for dusting off Pounce.

Regards Ian.

Above system called 'Diazo' printing.

Waste Ammonia from this system ideal for soaking Balsa wood for bending.

Edited By Circlip on 19/04/2023 10:21:09

If the collection to be scanned is in the thousands of items, then purchasing a scanner is likely to be worthwhile. The Midland Railway Study Centre has a 44" scanner which has been used for many different types of media; linen, tracing paper, vellum, printed posters, etc.

There were some reservations about it before its purchase was finally agreed, but the results have convinced everyone that it was a very worthwhile investment.

Ensuring maintenance of digital file types need to be built in to the collection's archiving policy.

If you're anywhere near Derby, you'd be most welcome to come and see what has been done at the MRSC.

Regarding preservation / conservation, 2 suggestions: 1) Try your county records office for advice. Some, like Norfolk, have their own specialist facility for conservation as well as providing general advice. 2) Are you an accredited museum - you might get some advice through the Museums Association.

As a Reprgraphic Technician I copied lots of different types of drawings in the 70’s and 80’s including the linen ones.

Some were put on film, 35mm, 70mm or Half Plate. Full size copies on paper or polyester were exposed on contact boxes and then processed. Cheap copies were made on paper or polyester on a Dyeline machine (Diazo process). A lot of work was done on a Statfile large format camera. An easel in front of the camera was swung horizontal and opened, the drawing was placed face down onto the glass and then the white plastic back of the easel was locked back in place. The easel was then swung back vertically for the photo to be taken. Illumination was by eight 2’ fluorescent tubes. The camera had 70mm and half plate roll film backs but could also take sheet film up to 12” x 10”.

The old original Blue prints (white line on a blue background) used to come through for copying from time to time. The were lovely looking drawings. The process ceased to be used long before I got into Reprographics in the mid 70’s. Many folks these days incorrectly call Dyeline prints (dark blueish purple line on a whiteish background) blue prints. We had a film studio ask us to produce a blue print for a James Bond Film once. After my boss laughed and said that process was long gone he did offer a modern solution. It looked nothing like a blue print but served the purpose. We made a full size negative of their drawing on polyester film then made a paper copy on our Dyeline machine. I still have a copy of it somewhere.

It’s not the same model but very similar to the camera I used:

I've had to do this numerous times for old drawings and when it was inconvenient to transport them across the country to the company's drawing office (where we had a large format scanner) have used local branches of Hobs Repro.

I think we were paying a couple of pounds per A0 sheet, for High-Res Scans same day turnaround.

If you don't want the hassle and risk of transporting the drawings, then one of my clients has used Flo Smart Solutions in the past to come in and do on-site scanning of hundreds of large format documents in one go.

Once everything is digitised, it's worth considering an agreement to transfer the originals to a suitable archival collection which can store them in a controlled environment for preservation.

Ideally such an agreement would see your organisation retain ownership and/or access rights in perpetuity, or offer a take-back clause where if the archive was unable or unwilling to store them, they would be returned.

Edited By Jelly on 19/04/2023 12:06:29

The DO that I ran had a very poor drawing stoore, cold and a bit damp. Storage was in conventional wooden flat plan chests. We had linen around 50 years old and very little degradation other than wear and tear was evident. We routinely printed drawings using the ammonia process with no harm. I think water is the one thing to avoid.

Martin

To all.

Many thanks for the advice.

The drawings are not damaged and will remain where they are except for two that will be copied for a talk. Our first job is to produce an index so that we know what we have. After that our problems start: we do not have any money and are not allowed to use cameras. Old fashioned blueprinting, using u-v light and potassium ferricyanide, has a definite appeal since it is cheap, safe and easy.

JA