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Time traveler here, stranded in the year of 1019 AD, medieval ages. Location: europe. While I can still access and post on web forums because my temporal transmitter has a 1Ky range, I have a broken solenoid. Thing melted down and it is part of my flux capacitor. And as a security measure my ship locked down and unaccessible until I can fix the solenoid. Stupid military protocols.

I am without access to any technology, just my portable temporal communicator (what you guys in the early XXI century would call a cellphone). I have to make do with tools and techniques from the locals.

I need to create another bobbin and all I have is copper wire. Naked copper wire and I don't need to tell that it would short-circuit the solenoid. Is there any way I can insulate the wire to repair my solenoid bobbin?

Many thanks.

P.S.: Don't worry about paradoxes. Nobody will believe this post is from a real time traveler.

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    $\begingroup$ Tree. From tree you have: resin, tar, cellulose, wood. Which are insulators. Seriosuly, I think that military protocol is there to keep you from geting back. You sure you finished your basic electric training? $\endgroup$ – SZCZERZO KŁY Nov 12 at 13:06
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    $\begingroup$ @szczerzokly 4D printing made the handling of electrical parts as useful in my time as your computers and paper printers did to transfer lettering. $\endgroup$ – Mindwin Nov 12 at 14:54
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    $\begingroup$ Come to XXI century (if you're able) and you will be amazed by all the DIY on transfering letters from printed paper onto other things. There is a serious design flaw in sending back in time people who don't know how to fix things in their time machine that have security protocols that lock it down if it's broken. Or you broken some security rules. You did didn't you? They told you "never go further than transmiter range to call for help because parts of time machine go into wibbly wobbly state" but noooo, you knew bettter than military science guys. $\endgroup$ – SZCZERZO KŁY Nov 12 at 15:09
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    $\begingroup$ This must be your first time out. Or you didn't believe the other gals about the paradox thing. Either way, just look in the basket beside the door; that's where you'll put the replacement bobbin after you get yourself out of this fix, along with the multitool that'll allow you to fit it. $\endgroup$ – Chris the Hairy One Nov 13 at 0:21
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    $\begingroup$ Caution: writing messages into a magic mirror and getting responses from the devils therein will surely result in a conviction for witchcraft. $\endgroup$ – Paul Nov 13 at 0:50

20 Answers 20

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The practice in the first half of the 20th century was to wrap wire in cotton cloth, resulting in something like a shoelaceDouble Cotton Covered Copper Wire Reels

from https://www.vycombe-arts.co.uk/onlineshop/prod_3699705-Double-Cotton-Covered-Copper-Wire-Reels.html
Alternately, pass your wire through wood resin, which will leave a fine insulating layer over your wire, good enough for low voltage work. The problem is that the resin will be sticky when wet and brittle when dry, so don't wind too tightly.

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    $\begingroup$ Just a tip for the cotton trick though: make sure you are not the person who has to pull the crumbling remains out of a wall in sixty years because the breakers keep tripping. $\endgroup$ – Borgh Nov 12 at 13:34
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    $\begingroup$ I thought at first it would be worse, but he's only a century or so too early for cotton in Europe. $\endgroup$ – Separatrix Nov 12 at 14:39
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    $\begingroup$ @Separatrix: Linen would work in a pinch. Then again, Italy and Greece are also in Europe, and Mediterranean trade existed in the BCEs $\endgroup$ – nzaman Nov 12 at 14:58
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    $\begingroup$ @puppetsock, wasn't everything in the middle ages done by hand and tedious and slow? Labor, unlike today, was the least expensive part of a product. $\endgroup$ – Ron Maupin Nov 13 at 4:28
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    $\begingroup$ This has a lot of upvotes from people that have never seen the thin wire and tight coils normally found in a solenoid. The question does say bobbin. Think about wire the thickness of a thread. $\endgroup$ – JPhi1618 Nov 13 at 16:06
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Beeswax

Expensive mind you, anything food related is, and you're cutting into the candle supplies of the wealthy, but beeswax is a good insulator, easy to work, and available in almost any historical period. Not suited for high temperature use.

Cloth

Also available in almost any period, though harder to work with for these purposes most cloths are reasonable insulators. Less temperature sensitive.

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  • $\begingroup$ I upvoted you. Cloth and wax (paraffin, etc) are still in use in nearly 100 year old telephone cable. Works fine in small gauge up to 300V. Paper is used as well, and lead for cable sheathing though those are beyond the question's scope. $\endgroup$ – geoO Nov 13 at 14:52
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I have done this. I have an interest in old technology and I recreate crystal radios, telegraphs and mechanical television.

When winding the solenoid you can seperate the windings by winding thread of similar diameter alternately with the wire (I used waxed sailmakers' thread). Once you get to the end of the coil former wrap a layer of paper (I used wax paper) around the coil and begin laying again.

For a solenoid this seperation should not cause a major issue as I'm guessing that you are using the solenoid as an electromagnet and not an inductor. If you are needing an inductor then you can use an online calculator to take into account the extra layering and the wider wire seperation.

I would also recommend coating each layer in wax before starting the next layer to prevent the wire from moving when you hit 88mph. The extra wax will act as extra insulation when handling the required 1.2 GW to activate the flux capacitor. The wax also minimises the build up of copper oxides.

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  • $\begingroup$ Would waxed parchment or cloth work instead of waxed paper for separating the layers? Our traveler landed in a backward area, rather than China where paper would have been available. $\endgroup$ – Patricia Shanahan Nov 14 at 3:41
  • $\begingroup$ Any insulating material would do. The main reason for waxing is to stop the material from absorbing moisture from the air and start to conduct so anything that insulates and can be waxed or oiled would work. $\endgroup$ – AndyW Nov 14 at 11:08
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    $\begingroup$ Hey, Andy, great answer and very practical. Except paper in 1019 is not a thing. I'll try using rabbit parchment and come back to you. Literally if it works. $\endgroup$ – Mindwin Nov 14 at 11:59
  • $\begingroup$ Wax is not a problem. Beeswax candles were the best available artificial light source. In use, the inner layers may get warm enough to melt beeswax, about 65C, but they will be stabilized and protected from moisture by the outer layers. The traveler might have to learn drop spindle spinning and get some unspun flax to get thread of the same thickness as the wire. $\endgroup$ – Patricia Shanahan Nov 14 at 13:20
  • $\begingroup$ @Mindwin On that note, any kind of paper or cloth will work. Vellum, for example. Just something not electrically conductive, which means you could even use dirt if you packed and dried it well enough (I don't recommend dirt). Cloth is probably your best bet. $\endgroup$ – thanby - reinstate Monica Nov 15 at 16:08
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You have copper wire. You need a thin insulating layer so that one winding does not contact the adjacent winding. This is easy.

Assuming you can produce the copper wire, you need to oxidize it in an acid solution. This will produce a green oxide layer which is insulating. Wind the green corroded wire with no overlap on each layer. Put a layer of silk or cotton or paper or fig leaf between the layers of wire.

The adjacent turns have very low voltage between them, so the insulation can be very thin. Some of the oxide may come off, but unless it comes off adjacent surfaces there is no short.

Copper oxide can be a semiconductor. (nb, I remember copper oxide rectifiers from my childhood.) The bandgap voltage is (from one source) 2-3 V, which for most frequencies and core materials is less than the turn-to-turn voltage.

If you have a high frequency for this coil, the volts-per-turn could be high enough to cause some conduction through the copper oxide. For DC, it isn't an issue.

Scrape off the green copper oxide insulation on the wire ends to make good, bright copper connections.

If you want to impregnate the coil with wax, go ahead, but you are probably in a hurry to get home.

For those wanting to learn more, this is a place to start. It differentiates between cupric-oxide and cuprous-oxide, which have different properties. This link discusses how to make copper wire into either oxide.

Simply exposing the wire to hot sulfuric acid doesn't leave copper oxide leaves copper sulfate, not one of the copper oxides. Copper sulphate is a salt, and as a salt, it may tend to be conductive when moisturized. If you get out something more blue (copper sulphate) than green (copper oxides), you should dry it well to eliminate any moisture. When dry, the salt should be non-conductive enough. You only need to use it once.

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  • $\begingroup$ This is slick. Have you got links describing this method in use or did you invent it? Slick either way. $\endgroup$ – Willk Nov 13 at 19:32
  • $\begingroup$ I looked at the conductivity of copper oxide, and it is non-conductive. $\endgroup$ – cmm Nov 13 at 21:33
  • $\begingroup$ It's pretty easy to test if it worked. Measure the resistance of the wire before you wind it, then after. If the resistance changes, you have a short (insulation problem). $\endgroup$ – Scott Whitlock Nov 14 at 12:51
  • $\begingroup$ this would be a very clever way to do it... and something that could be easily done.. however I haven't heard of this ever being done ... would love to see some references or at least some literature suggesting it can be done ... as @Willk said "This is slick." :) $\endgroup$ – Afrah_Rahman Nov 15 at 4:36
  • $\begingroup$ It would never be done now. I doubt it was ever the case that the ability to extrude copper through a die (to make a usable wire) existed when thread making did not preexisting, making the "wrap it in thread" method available. Early in my RF life, I had a roll of Litz-wire that was thread wrapped. But were I a time traveler stranded in a past that had copper but didn't have insulated wire, this would be a way. It wasn't the path our tech took, but to could be a path. $\endgroup$ – cmm Nov 15 at 11:55
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Lacquer is an alternative. It comes in many thicknesses. It's not too expensive. It can be painted on then heat cured. There are many different types that can stand up to a variety of challenges such as wear, heat, cold, even limited bending.

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    $\begingroup$ It might be a bad example for this particular use case, as you have to insulate the wire before winding it and lacquer would crack. If you have any wire that you could insulate in place though, it's not a bad option. $\endgroup$ – Turksarama Nov 13 at 0:04
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    $\begingroup$ "Other types of insulation such as fiberglass yarn with varnish, aramid paper, kraft paper, mica, and polyester film are also widely used across the world for various applications like transformers and reactors. In the audio sector, a wire of silver construction, and various other insulators, such as cotton (sometimes permeated with some kind of coagulating agent/thickener, such as beeswax) and polytetrafluoroethylene (Teflon) can be found. Older insulation materials included cotton, paper, or silk, but these are only useful for low-temperature applications (up to 105°C)." $\endgroup$ – Mazura Nov 13 at 0:33
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    $\begingroup$ en.wikipedia.org/wiki/Magnet_wire $\endgroup$ – Mazura Nov 13 at 0:33
  • $\begingroup$ If you lacquer paper or cloth and only heat it after it is wound it should work well. lacquer does take a long time to dry, easily long enough to wind the wire. $\endgroup$ – John Nov 13 at 14:35
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Enamel

Thin copper wires--like those used in inductors, transformers, motors, etc.--are enamelled. This is known in the modern world as magnet wire. Surely, you would prefer enamelled wire for your solenoid bobbin.

We know that enamelled objects existed as early as the 13th century BCE.

A concise history of enamel.

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    $\begingroup$ While enamel isn't a great solution in the general sense, it's exactly the correct solution for this specific problem since OP is building a solenoid. You need your coils wrapped tightly and densely, which is difficult with most of the other solutions. $\endgroup$ – bta Nov 13 at 0:47
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    $\begingroup$ This sounds like a good answer at first, but Wikipedia says about enameled wire: "The insulation is typically made of tough polymer film materials rather than enamel, as the name might suggest." So maybe not. $\endgroup$ – kwc Nov 13 at 3:42
  • $\begingroup$ Maybe a basic polymer could be easily made? Like the kind that comes from over-heating oil, better known as seasoning (for cast iron). $\endgroup$ – IronEagle Nov 13 at 6:52
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    $\begingroup$ @IronEagle linseed oil polymerises, and has long been used to waterproof fabric. $\endgroup$ – Chris H Nov 13 at 10:09
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    $\begingroup$ @kwc - That doesn't mean that actual enamel wouldn't work. It only indicates that the modern materials are better in some way (more flexible). Before these materials were invented, actual enamel was used. $\endgroup$ – bta Nov 13 at 23:19
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Think Trees

Gutta Percha , Latex , and Amber are reasonable insulators. Wrap the wires in various tree saps, and dry the covering over fire. Don't dry all the way, nor burn it, or it becomes inflexible. When working on the electronics, use dry clean wooden tools to avoid sparks and conduction.

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  • $\begingroup$ Gutta percha is the right stuff. qz.com/785119/… $\endgroup$ – A E Nov 13 at 15:25
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Paper?

Paper may not have been invented (or be readily available) yet, but it can be made with available tools and materials. Paper is used as an insulator in our time, so could work for you too - it's a good insulator and it provides physical separation. It does require you keep it dry though - but you could coat your work in wax when finished if moisture is a problem. If you're using lots of current, you may need to consider cooling too (although less so than if you use wax as your insulator).

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  • $\begingroup$ paper was invented long before the medieval time period. . $\endgroup$ – John Nov 13 at 14:33
  • $\begingroup$ @John invented yes, but not known/made in medieval Europe prior to c.1080. en.wikipedia.org/wiki/History_of_paper#Paper_in_Europe $\endgroup$ – Gnudiff Nov 13 at 17:44
  • $\begingroup$ Thanks - I got my dates way wrong, so have edited to reflect fact a little better. The availability of paper is the real issue, rather than invention though, but point taken. $\endgroup$ – Ralph Bolton Nov 14 at 9:24
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Not mentioned yet, but leather is also a good insulator.

So there are plenty of options, most likely you'd want a combination of them for optimal effect of course, and to reduce the mess (resin gets sticky, so wrap the resin coated cable in cloth and wrap that in leather because the cloth is vulnerable to mechanical damage for example).

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Mentioned before leather. Intestines (small-large) best leather for a wire coating. Already a tube just pull it tight and let it dry. Smaller animals smaller tube.

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  • $\begingroup$ Not a bad first post, though it's quite short it's apt. When you have a moment, please take the tour and read up in the help center about how we work. Welcome to the site. (From review). $\endgroup$ – We are Monica. Nov 13 at 18:04
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In addition to the great answers so far, wax in general is usually an insulator, so a nearby candle or rendered animal fat might do the trick.

If you don't want to kill an animal, or can't find a candle, then you can use wool. Really any type of fur or silk would do, but wool is a decent insulator, and would almost certainly be available in medieval Europe.

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I think you could use grape juice thickened with flour. Both materials should be available in a medieval context (and long before that). It dries to a rubbery texture and you could run the wire through a trough of it a few times to ensure full coverage.

To get an idea of the finished appearance, consider Georgian Churchkhela. You would want it thinner, of course, and well dried to avoid excessive conductivity.

enter image description here

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Pitch and cloth or paper.

the first widely used insulated wire was insulated with asphalt (pitch) soaked cloth. both materials are available in a medieval setting. pitch is widely used by shipbuilders and a dozen other trades and cloth is a bit expensive but not prohibitively so especially for how little you need. Cotton cloth is expensive but nearly and form of paper or thin cloth will work, even collecting worn rags will work as long as you wash them first. this is really just acting a a physical carrier/spacer to keep the pitch between the wire while you wind it tightly.

pitch is sticky which you don't care about, if it picks up sand or grit it only becomes a better insulator, it is waterproof which is a bonus, and stays nice and flexible. if you try to ue it for years it will corrode the copper, but this is a fix to get you to someplace you can buy wire not a permanent fix.

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  • $\begingroup$ This was my thought initially. Pitch on its own might work, or pitch combined with any kind of reinforcement like cotton, wool, or even horsehair. Horsehair seems likely as it was commonly used in upholstery, crafts, or reinforcing the plaster in the walls of old houses. I've seen the latter in our family's old victorian-era house. $\endgroup$ – cleaver Nov 13 at 22:27
  • $\begingroup$ @cleaver really you just need something to keep the pitch from being squeezed out by winding. you could even use crushed straw dust, $\endgroup$ – John Nov 14 at 13:17
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Wax boil/VPI that solenoid

Suppose you have a V volt solenoid with N coil windings laid out in L layers.

In solenoid windings, you only have very low voltage between adjacent windings - just V/N. Thus, a simple varnish will suffice for wires in one layer.

Between each layer, you have 2*V/L voltage, and you can use wax-impregnated cloth between the layers, or mylar salvaged from the rebuild - this being more important on the end of the layer that doesn't cross over.

If, at this point, you can build a nonferrous metal "can" to enclose the solenoid, that'd be great. That will help the solenoid stay solid with wax even if it gets hot enough to melt the wax.

Now, get a vat of wax to 212 F, and dip the solenoid in it. Or if you've done the can thing, that can be the vat. This will boil all moisture out of the coil windings. If possible, draw a vacuum on the vat to force all the air and steam to vacate the coil windings. You could simply release the vacuum and wax should be driven into the voids left by the vacuum; however if you can pressurize the vat, that will help.

Let it slowly cool down to let the wax freeze.

Congratulations, you have just done VPI (Vacuum Pressure Impregnation) in 1019 A.D.

Now the tricky part, remelt the wax just enough to get the part free of the wax, but not so much as to melt the wax out of the windings, which would undo our work! This is where that metal can would come in handy.

Now, you should have done all this stuff with epoxy instead of wax, but you didn't want to bring any epoxy. "It's just a day trip" you said.

Insulated boards

Now, if you need objects insulated, get maple wood. It has the best insulating characteristics of any reasonably available wood. Mill the maple down to rough dimensions, and then stick it in the wax boil for a day or two. A vacuum cycle or two wouldn't go unappreciated. You are boiling all the moisture out of the maple and replacing it with wax.

Same deal with letting it fully cool then reheating it just enough to get the wood out of the wax.

This will cause dimensional changes in the wood, which is why we waxed it "rough" before we did our woodwork. Now, have your woodcarvers do their thing. Finally, give it one more night's boil-and-freeze to make sure wax fully penetrates all the freshly exposed wood surfaces.

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    $\begingroup$ Maple wood in Europe in 1019? $\endgroup$ – Peter Taylor Nov 13 at 9:34
  • $\begingroup$ @PeterTaylor there are several native European maple species, e.g. Acer pseudoplatanus (called the sycamore in Europe), A. campestre, (field maple or dog oak), A platanoides, (Norway maple), etc. Sycamore is commonly used for high quality woodworking, e.g musical instrument making. $\endgroup$ – alephzero Nov 13 at 15:54
  • $\begingroup$ @PeterTaylor Dammit Jim, I'm an electrical guy, not a tree doctor! $\endgroup$ – Harper - Reinstate Monica Nov 13 at 16:02
  • $\begingroup$ Sycamore: Interesting. I didn't realize it was a European native - probably didn't reach GB until 1500 though. $\endgroup$ – Martin Bonner supports Monica Nov 14 at 12:12
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Use varnish to coat the wire. You can get it from a cabinet maker. I've done this before and it works.

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  • $\begingroup$ It's short but it holds together, both cabinet makers and varnish are plausible in period. $\endgroup$ – Separatrix Nov 14 at 14:02
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Why not just go down the modern route, and coat your drawn copper wire with cresol lacquer, derived from coal tar or creosote? These substances are reasonably commonly available, and have been known for thousands of years, from the pre-Christian era.

Having worked (albeit briefly) in quality control at a factory producing copper transformer wire - exactly the thing that the OP wants, I can state with some authority as to just how copper wire is coated today.

A modern wire factory both draws the wire and coats it, though the process of drawing the wire may easily be separated from the process of coating it.

In essence, the drawn wire is passed through a metal die with an opening slightly larger than the diameter of the wire. Just before the wire passes through the die, a liquid mixture of phenols and cresols (which is pretty much just filtered and fractionated coal-tar or creosote, diluted as necessary by turpentine, which is itself a light phenol-like compound sourced from the Turpentine tree) is poured continually over the inwards-face of the die, and is spread along the length of the wire as it passes through the die (remember that the die has a greater diameter than the wire). On the reverse side of the die, the coating is still wet and sticky, however heat treatment (in a modern factory, achieved by passing the wire up and down through a tower kept at a high air temperature of around 70°C+ for several minutes) causes the lighter solvents to evaporate, leaving behind a dry, non-sticky, solid and flexible coating. Using higher temperatures to drive off the light solvents more rapidly is not advisable, since the boiling solvents cause pitting in the coating, effectively compromising the integrity of the insulation.

All that remains after the coating has been applied and dried is to wind it onto a spool for storage before it is put to its final use.

This coating, while ideal for its purpose and very easy to apply, does have its drawbacks. The chemicals involved are toxic respiratory irritants, and can cause severe bronchitis in some of those exposed to it. I can attest to this from personal experience: I turned out to be susceptible, and developed bronchitis within three days of exposure to this environment. However, on ceasing to be exposed, the condition clears up within a few days. This is probably a small price to pay to be able to produce the needed insulated transformer wire.

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You can fabricate a crude form of cellulose acetate which is a form of thermoplastic. It can be created with cotton and other natural fibers and concentrated vinegar aka acetic acid. Both of these substances would be relatively easy to obtain.

If the solenoid can be activated by mechanical means instead of electrical. That is moving the piston by another way to engage the contact. This is also an alternative to avoid having to rebuild the solenoid thereby avoiding the need for copper wire and an insulator. A little bit of creative engineering.

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You need a MIX of solutions. Your solenoid needs to have many windings, which means multiple layers. Traditionally, wax-paper was used between layers, and I believe still is.

The next insulator is spacing. On your innermost layer, use a slightly larger diameter wire, not for conductivity, but to set the spacing of all subsequent layers. Now they won't be touching.

As you wind all layers above each other, they will naturally space apart to align with the layers above them, so the wires will not touch those laid next to them.

To ensure this, paint a layer of laquer, paraffin wax or other insulant over each layer. This will also make the wax paper layer stick better, which will make winding the next layer of wire easier.

This should allow a large number of very fine, tight windings.

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Send me the technical details of your temporal communicator and I'll make one and relay your message for you to your original time and they can send a rescue party to you with a spare solenoid... and it doesn't matter to you if it takes me a few years to complete the build as you'll still be rescued shortly after you send me the details!

Alternatively, you can make isinglass from fish swim bladders (after all, that's a waste product, no-one will mind if you collect some fish guts from a midden) and coat the wires in isinglass. It's a kind of fish-based gelatin and will make a nicely coating substance that when dry will be non conductive and flexible enough to wind the wire afterwards. For added electrical security, if you have space in your solenoid bobbin, before it's quite dry you can coat the isinglass with some finely ground quartz... or any other non conductive dust to give an extra layer of insulator to prevent shorting in the solenoid. Once wound and tested, coat the entire bobbin in melted beeswax to ensure it stays dry even if you run across an inter-temporal rainstorm

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  • $\begingroup$ You need 1g of Nihonium. Get that and we'll talk. $\endgroup$ – Mindwin Nov 14 at 15:28
  • $\begingroup$ Ah, I'd missed that element being created. I'll get collecting. $\endgroup$ – houninym Nov 14 at 15:42
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Distilled water is quite a good insulator, easy to produce with tools you probably already have, and readily-available in both liquid and solid phases.

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    $\begingroup$ It doesn't work quite so well as insulation though. $\endgroup$ – DKNguyen Nov 12 at 23:12
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    $\begingroup$ because the insulation in windings need to provide physical separation between the windings. $\endgroup$ – Jasen Nov 13 at 8:32
  • $\begingroup$ Doesn't work for a solenoid bobbin. The wires will touch each other. -1 $\endgroup$ – Mindwin Nov 13 at 19:00
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    $\begingroup$ Also the copper wire will add ions to the water and insulator effect will diminished $\endgroup$ – Old_Fossil Nov 14 at 5:56
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    $\begingroup$ Resistivity of distilled water is 0.18 MΩm, resistivity of air is at least 13PΩm (it depends on the humidity. P = peta = 1 million billion). See this table That is a difference of ELEVEN orders of magnitude. Why on earth would you use water when you could use air? (Neither are suitable in this application because of the need to preserve physical separation of course.) $\endgroup$ – Martin Bonner supports Monica Nov 14 at 13:37

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