Shellac insulating varnish

[ScottBouch]

Hi all,

As some of you guys no doubt have had experience of re-winding transformers, aerial coils, inductors, relays, etc.. Does anyone have any specifications or supplier/brands of the types of Shellac used in electronics in the mid century?

And are these types still availavle today? If so, where from?

Looking online has given me a headache, so I thought it beat to just ask directly to those with experience.

In the 1950's / 60's military avionics I mess with, I sometimes see what I assume to be shellac (translucent light brown varnish) applied as small spots to soldered joints (possibly as an inspectors marking), and also applied over painted characters such as serial numbers on chassis. Plus the windings of transformers, relays, etc... Additionally used on knots of cable harness lashing, and sometimes on threaded terminal post nuts as either a witness marker of them loosening, or possibly to act as a bit of a threadlock.

Cheers, Scott

[ScottBouch]

I seem to have poted this in the wrong place - I could have sworn I posted it in Components and Circuits, but as my question is nothiing to do with cabinets please can a modeator move this thread to either:

Components and Circuits, or Genera Vintage areas?

Many thanks, Scott

[Radio Wrangler]

Thread moved.

You'd not allowed for windage and gravity, hitting the section below the one you were aiming for.

My aim's approved amazingly over the weekend. I now have two functioning eyeballs. Thank-you, NHS.

David

[David G4EBT]

Shellac is a resin secreted by the female lac bug on trees in the forests of India and Thailand, which is harvested and refined. It varies in colour from light blonde ("platina") to a very dark brown ("garnet"), with many varieties of brown. The colour is influenced by the sap of the tree that the lac bug is living on and by the time of harvest.

Flakes of shellac are dissolved with denatured alcohol (methylated spirit), and mostly sold ready mixed as French polish, sanding sealer and knotting. I think to use it for the purposes that you wish to use it, any of those might be a bit too thin, so a better option might be to buy shellac flakes and experiment with the dilution. EG, for French polish, typically 25 grams of flakes would be dissolved into 100ml of methylated spirit, so maybe 50/50 would be a good place to start? Say 1 teaspoon of flake and one of meths till you get the consistency to what you’d like.

Here is an example of flakes you could buy:

https://www.ebay.co.uk/itm/325515384...xoCEzAQAvD_BwE

If you feel that would be too much of a faff or too pale, (you aren't making a violin after all!), you could buy a small 35ml tester pot (or 100ml for the same price), of ready made garnet (brown) quite cheaply at this link to see if it fits the bill:

https://www.ebay.co.uk/itm/325271073...Cclp%3A4429486

Hope that might help a bit.

[Craig Sawyers]

That is furniture shellac - the stuff that comes from the lac beetle. It is dissolved in ethanol for application, which is why putting glasses containing alcoholic beveragess with wet bases leaves unsightly rings on high grade furniture.

There is a confusion between that and the identically named shellac varnish that is used to impregnate transformers and tropicalise. Or indeed "shellac" which is the name of the thick stuff that ladies pay to have put on their fingernails and toenails, and you almost need a Dremel to remove.

Craig

[ScottBouch]

Hi Craig and David,

All interesting stuff thanks!

Yes I am certainly interested in the types of shellac used in electrical engineering as an electrical insulator.

I thought exploring brands / suppliers or specifications of the 40's, 50's , 60's may point me at the right types that were used back then. (especially pertaining to aviation)

[M0FYA Andy]

Craig, are you sure that the shellac used in furniture polish and that used in electrical shellac varnish isn't the same stuff? I confess I have always assumed it is!

Andy

[ScottBouch]

So far have found on Dave's wonderful website that A.Macnair & Co Ltd supplied shellac, but I can't find much more info on them:

https://aviationancestry.co.uk/?sear...9&endYear=1990

Cheers, Scott

[Goldie99]

I was under the same impression Andy.

Having experienced a 1950's M'cycle Magneto with breaking down Shellac insulation (Mag works fine when cold, not at all when hot), I would recommend more modern replacements unless it's for entirely cosmetic purposes. Maybe worth checking something like 'Dolphon CC1305' or similar, I know that one was used in Magneto repair.

Alan

[ScottBouch]

Hi Alan, my purposes are nothing like the demands of a magneto - 28V DC at the most. I can see why you went for a modern alternative.

As I'm not doing any transformer re-winds etc.. most instances of shellac in this equipment I'm working with are either as:

- An inspectors marking (small dot on soldered joints or side of terminal screws/nuts).
- Witness to a disturbance (small dot on soldered joints or side of terminal screws/nuts).
- Protective lacquer over painted labelling.
- Setting knots in cord used for cable harness/loom lashing, or component tie-down lashing (some components are mechanically tied down (or clipped/clamped) due to aircraft G forces).

Basically if I need to repair a piece of equipment it's nice to be able to return it to its original state when completed, dabs of shellac on the sides of screw heads and all..

It may seem like I'm asking an overly detailed question here as the stuff used may well be similar to furniture shellac, but reading the below article reveals a few different types of processed shellac for different purposes (waxed, de-waxed, food grade, bleached, bleached and de-waxed):
https://www.afsuter.com/product-category/type/shellac/
I'd love to know which would be most suitable, to match the original shellac type used in engineering and electronics in the post-war period.

Cheers, Scott

[The Philpott]

I've noticed shellac on solder joints seems to protect them from becoming slightly furry with corrosion. I've seen WW2 joints that are still shiny when the shellac is flicked off.

Dave

[Uncle Bulgaria]

I am not aware of any additives for different purposes, though perhaps there were some advanced compositions around in WWII. The alcohol it is dissolved in evaporates leaving the deposited shellac, which has taken on the shape of the surface. The varieties you're concerned about in post #10 are really only of interest for finishing. For example, as it naturally is brown, food preparation may want a clear version so it merely makes the underlying colour look glossy (sweets, pills...); likewise something that's going to be painted will need wax removed for adhesion of the paint.

For ancient electrical purposes I would be almost certain that it is just the cheapest option straight out of the beetle, as the preparation processes for de-colouring won't affect the electrical properties. For a 1920s voltmeter I used shellac on both the electrical connections as you're planning to do, and to polish the case!

Shellac was used for innumerable purposes up to the mid-C20th as it's generally fabulous for coating things impermeably. It was indeed used for nail varnish before acrylics came along, so I guess the term stuck (along with the mostly US usage 'to give someone a shellacking', which this BBC article suggests is possibly linked to similar uses in the UK of 'pasting' or 'plastering').

All the electrical uses I've seen have been riffs on brown, so I would use shellac flakes in alcohol, with the solution painted onto the object and left to dry (or dipped if you're going wild). You'll need several coats depending on the thickness of your solution, as David G4EBT mentions. I have used it myself for an old transformer where I checked the original varnish was shellac by painting an area with alcohol and seeing if it rubbed off.

[ScottBouch]

Thanks for that!

Regarding an alcohol, would IPA work for this (as I have some), or am I best to find some ethanol?

Cheers, Scott.

[ms660]

Shellac was also an ingredient in RCA's basing cement amongst others.

Lawrence.

[Silicon]

In the post war period they may have used the term 'shellac' for polyurethane and polyester varnishes.

Can you remove your post war varnish with alcohol?

[G.Castle]

Originally Posted by ms660

Shellac was also an ingredient in RCA's basing cement amongst others.

Lawrence.

Yes. Often mixed with wood flour or asbestos as a filler adhesive. Very effective alternative to 'waterglass', (sodium silicate).

[G.Castle]

Originally Posted by ScottBouch

Thanks for that!

Regarding an alcohol, would IPA work for this (as I have some), or am I best to find some ethanol?

Cheers, Scott.

It does dissolve shellac and once the IPA has evaporated it would have the same effect as mixing it with acetone ie. set to a hard varnish.

I've used IPA to free off shellac sealed threads before now.

[Bazz4CQJ]

As per post#4 Scott, I think that methylated spirits is preferred and IPA may not be optimum

B.

[M0FYA Andy]

A good pal of mine, sadly no longer with us, served his apprenticeship with the GPO telephone service back in the days of Strowger exchanges. He was an expert at refurbishing damaged PO3000 relays, or building up a particular combination of coil and contact types as required. When the relay was complete, he would varnish over the screws holding the contact assemblies together with shellac varnish he mixed himself from shellac flakes dissolved in methylated spirit. I wish I could still ask him what variety of shellac flakes he used!

Andy

[ScottBouch]

Hi Andy,

Sorry for the loss of your pal, but thank you for the advice on his use of methylated spirit with the relays (PS: there is a slugged 3000 series relay used in the engine starter system of the EE Lightning aircraft to provide a short time delay, making this nicely relevant to this project!).

There does seem to be a reoccurring issue I'm facing with restoring 50's/60's avionics kit; to be blunt, there simply aren't many people left from that era. I'm busy collecting up what information I can now from those who are still with us - there really is no time like the present to ensure this knowledge lives on.

Back on topic, would there be any difference between dry flakes / solution in terms of shelf life?

Cheers, Scott