photochromic pigments from mindsets

UV reactive materials, which initially have an off-white appearance, change to bright colors when exposed to UV rays (sunlight or a UV lamp) and revert to their original pale color when away from UV light. The basis for these materials are photochromic pigments which can be mixed with an acrylic base and then applied as normal paint. The more dilute the pigment, the less dramatic the color change.

acrylic base to orange photochromic pigment ratio tests ran by a student of the Aix-en-Provence (France) Art School

Besides pigments, which can be used to make color-changing paints, photochromic materials are also available in the shapes of sewing and embroidering thread, plastic goods such as beads and buttons, and nail polish. Naturally it’s also possible to produce photochromic fabrics, but I haven’t been able to find them as raw materials in retail shops.

photochromic thread and beads (indoors and outdoors)

What is it exactly?
According to Wikipedia:

Photochromism does not have a rigorous definition, but is usually used to describe compounds that undergo a reversible photochemical reaction where an absorption band in the visible part of the electromagnetic spectrum changes dramatically in strength or wavelength. In many cases, an absorbance band is present in only one form. The degree of change required for a photochemical reaction to be dubbed “photochromic” is that which appears dramatic by eye, but in essence there is no dividing line between photochromic reactions and other photochemistry.

Suppliers
:: Mindsets (UK): photochromic pigments and sewing thread
:: Solar Active (USA): UV reactive sewing and embroidering thread, plastic goods (beads, buttons, etc.), nail polish

Share your knowledge
If you’d like to contribute content or corrections regarding UV reactive materials, please use the comment form below.

>> about the materials 101 series.

As the name indicates, electrotextiles are textiles with electrical properties. They’re mostly used for electromagnetic shielding, anti-static and heating purposes, and also for soft circuits: electric circuits or sensors made out of a combination of special fabrics, threads, yarns and electronic components.

:: conductive fabrics
:: conductive threads & yarns
:: special electrotextiles
:: related materials
:: starter kit
:: electrotextiles tutorials by openMaterials
:: learning resources
:: main suppliers

Conductive Fabrics
Fabrics with electrical properties made by blending or coating textiles with copper and/or nickel and/or silver fibers. They’re available in many textures, weaves and combination of materials. Stores such as Plug & Wear, Mindsets and Less EMF sell kits with a sample of each of their conductive fabrics. These samples provide an excellent way to get a hands-on feel for and test the properties of each material in order to find the right one for your project before acquiring it in a larger quantity. There are many types of conductive fabrics and you can find an extensive (though not comprehensive) list on the oM wiki. Here I will only describe some of my favorites.

:: Shieldit Super (iron-on conductive fabric) from Less EMF: a single side conductive fabric made of polyester substrate, nickel and copper. The back side is covered with a non-conductive hot melt adhesive, which activates at 130ºC (266ºF), meaning that it can be ironed on to another fabric, wood, glass or paper. This fabric is a pretty good conductor, easy to apply and thus perfect for making longer connections between components. It can also be cut and sewn like ordinary fabric. 230 g/m², 0.17 mm thick. UL 94V-0 level flame retardant. RoHS Compliant. Gray, 14 inch wide.

:: Electrolycra from Mindsets: looks and feels like ordinary lycra but it’s highly conductive. Its conductivity in one direction depends on how tightly it is stretched – if you pull it the resistance increases and then drops again when stretched even tighter. When cut into a thin strip, the material also warms up when current is passed through it and can thus provide the basis of a heated garment. A 6V battery will cause an appreciable warming effect. Resistivity: 5 ohms per 100mm, increasing to 20 ohms when stretched to 150mm. If the material is turned through 90º and stretched the resistance drops to 2.5 ohms.

:: Knitted Superlight Conductive Fabric from Plug & Wear: an extremely light and transparent conductive fabric, only 190 g per sq.m. It allows air flow and is easy to cut with scissors. It can also be sewn with a standard sewing machine or soldered to. Hand washable. Material: tin copper. Resistivity: 0.1 Ohm per square. Width: 1000 mm (39″), thickness: 1 mm (.039″), max working temperature: 150°C (302°F), weight: 190 g per sq.m.

:: Conductive Aluminum Laminated Fabric from Plug & Wear: a single side conductive (the shiny side) laminate made of aluminum foil and fiberglass reinforced polypropylene tape. It’s easy to cut with scissors and it can be sewn with a standard sewing machine, but it’s very stiff and calling it a fabric is a bit of a stretch. In fact it feels a lot more like a thick aluminum foil which makes it perfect for paper projects. In a recent openMaterials workshop, a group of students cut it into an beautifully intricate shape and used as a touch sensor on the cover of a book. Width: 650 mm (25.5″); thickness: 156 micron; max working temperature: 45°C (113°F); weight: 185 g per sq.m.

:: Velostat: a film made of opaque, volume-conductive, carbon-impregnated polyolefin. The resistivity of velostat decreases when pressured. When sandwiched between two conductive layers, it has a wonderful range for making pressure and bend sensors. Depending on the project, more than one layer of velostat might be necessary, eg. I used 3 layers of velostat to make a pressure sensor that gradually lights up a few strands of EL wire. Thickness: 100 microns; width: 91 cm (36″). Volume resistivity < 500 Ohms/cm. Color: black.

Conductive Threads & Yarns

Conductive threads are made of a combination of either cotton or polyester with alloys of several conductive materials such as silver, copper, tin and nickel. Just as most conductive fabrics, conductive thread is uninsulated making it excellent to connect electronic components to each other or to other electrotextiles. In order to ensure proper connection it should be sewn very tight and with more loops than normally used with regular thread. After some time, conductive thread tends to fray and the stitches to become loose. For this reason I often coat my conductive thread connections with a bit of Wire Glue. Wire glue takes several hours to cure so this coating should only be done after you’re done with all the sewing.

There are several kinds of conductive thread, with significant differences in terms of conductivity/resistivity and fraying, but they are commonly sold in two qualities: 2-ply and 4-ply. The 4-ply contains twice as much metal as the 2-ply, making it more conductive, but it’s also thicker making it harder to thread and sew with. For this reason I usually keep a set of sewing needles with large eyes. The How to Get What You Want and Fashioning Technology websites have some excellent overviews and comparisons of the conductive threads available in the market.

The resistivity of all conductive threads increases drastically with length, making them inappropriate for long connections. For this reason, consider making long connections with ribbons of a good conductive fabric and using the thread only to sew the electronic components to the conductive fabric.

The highly resistive (<1000 Ohm/10cm) silver plated thread offered by Less EMF (cat. #A1226) is good for embroidering fixed or variable resistors.

Conductive yarns are usually made of a combination of polyurethane and inox steel fiber. The resistivity of some yarns increases when the knitted piece is stretched. Again, see How to Get What You Want for great information on conductive yarn.

Special Electrotextiles
:: Textile Perfboard: a fabric base with interlaced rows of thin metal wire.

:: Pressure and Bend Sensitive Fabrics, Tapes and Buttons: made of a layer of insulating knitted or resistive fabric sandwiched between two layers of knitted conductive fabric.

:: Textile Water/Wetness Sensor: detects water by changing its resistance from an open circuit to a few megaohms.

:: EL Wire Tapes: knitted tapes with strands of EL wire weaved into them.

:: Hook and Loop Fastener: similar to velcro but conductive.

Related Materials
:: Wire Glue: even though originally created to replace solder on the connection of electronic components, wire glue is a great material for working with electrotextiles as well. I use it to coat conductive thread knots to prevent them from fraying and also to attach metal snaps to metals that can’t be soldered to.

:: EL Wire: can be basted, woven into or otherwise applied to your soft circuits for illumination.

:: Quantum Tunnelling Composite (QTC): an interesting pressure sensitive material for making textile control pads and keyboards.

:: Metal Sewing Materials: almost all metal sewing supplies, such as snaps and zippers, are conductive and can be used in conjunction with electrotextiles. See oM’s connecting hardware & softwear on soft(er) circuits blog post for some examples.

:: SMD Components: SMD battery holders, LEDs, etc that have flat metal pads are also great for soft circuits. You can solder or wire glue metal snaps or metal rings on these pads to attach them to your circuit.

Starter Kit
I’m often asked what are the first materials one should get to start making soft circuits. Here’s a suggestion for a starter kit:

:: Conductive thread
:: Iron-on conductive fabric or another non-stretch conductive fabric*
:: Stretch conductive fabric*
:: Velostat*
:: Assorted LEDs
:: CR2025 or CR2032 lithium batteries
:: SMD lithium battery holder with flat pads such as this one
:: Non-conductive fabric (felt is my favorite)
:: Sewing supplies: thread, metal snaps, needles with large eyes, needle threader
* Most electrotextiles stores sell conductive fabric sample kits, you can just try one of those instead of buying a larger quantity of the stretch and non-strech conductive fabrics.

Electrotextiles Tutorials by openMaterials
:: Connecting Hardware & Softwear on Soft(er) Circuits
:: Light Up Handshake Glove

Learning Resources
There are many resources for learning how to use electrotextiles. One of the most useful and complete, from a materials and experimentation point of view, is Kobakant’s How to Get What You Want – make sure to check out the sensors and conductive materials sections.

:: Websites w/ Tutorials
Fashioning Technology
How to Get What You Want
Lynne Bruning’s Techniques
Plug & Wear
Plusea
Soft Circuits Saturdays
Sternlab

:: Books w/ Tutorials
Fashion Geek by Diana Eng
Fashionable Technology by Sabine Seymour
Fashioning Technology by Syuzi Pakhchya
Open Softwear by Tony Olsson, David Gaetano, Jonas Odhner, Samson Wiklund
Switch Craft by Alison Lewis

:: Other Interesting Websites
3lectromode
Talk2MyShirt

Main Suppliers
:: Less EMF (USA): conductive fabrics, resistive thread, hook and loop fastener, textile pressure sensitive switches, fabric potentiometer kit

:: Mindsets (formerly MUTR) (UK): conductive fabrics & thread, but make sure to also check out the materials > smart materials section

:: Plug & Wear (Italy): conductive fabrics, textile perfboards, pressure sensitive fabrics, tapes and buttons, textile water/wetness sensor, conductive thread and yarns, EL wire, EL wire tapes

:: Sparkfun (USA): several types of conductive thread

Share your knowledge
If you’d like to contribute content or corrections regarding electrotextiles, please use the comment form below.

>> about the materials 101 series.

Treehugger recently reported on BioCouture, a fashion research project based at Central Saint Martin’s College in London and led by Suzanna Lee, which seeks to grow textiles from a vat of liquid:

The process uses a sugary green tea recipe, to which, a bacterial culture is added. It takes about 2-4 weeks to grow a sheet that is thick enough to use. Sheets are then dried down; either shaped over a wooden dress form–like the ghost dress and ruff jacket –or sewn together conventionally. Depending on the recipe the material can either feel like paper or–more desirably–like a vegetable leather.

In testing with dyes we found no need for mordant [a substance used for dyeing fabrics] and an incredibly small amount of dye goes a long way so it’s eco-credentials go through the entire process. We also recycle a percentage of the fermentation liquid.

vegetable leather grown from a vat of green tea

We look forward to more information about the project and the process. Read more about it at treehugger.

Thanks Rob for pointing this out :)

I keep thinking that even though we tend to use conductive fabric and other soft circuits materials mostly for wearables and such, there has to be much more to it than that. Ayman’s drumsticks are a great of example of other interesting applications for these materials. He made them for his iPad iSteelPan application, but they’ll work on any capacitive surface.

The iSticks are made out of pure copper polyester taffeta fabric (I bet conductive lycra would work really nicely too), metal rod, string, and cotton pads. Check out Ayman’s instructable and make your own!

(via Alicia Gibb)

I’ve learned that there are 3 main challenges in working with soft circuits. The first one is to create circuitry with materials that are almost always completely exposed: a lot of thought goes into the layout of the circuit to not only avoid accidental shorts during normal wear, but also to avoid crisscrosses between conductive materials within the circuit layout. The second one is to think in 3D: more often than not your circuit can’t be applied to a single flat surface and you have bits and pieces spread out over several areas or layers of the piece. The third one is to find ways to connect hardware with soft conductive materials: sometimes you just need to use hard electronic components or a board.

The first two challenges have to be addressed on a case by case basis, but I’ve been experimenting with some methods to address the third that might be useful to others – I’m also hoping for suggestions on different methods and/or ways to improve these :)

:: The curled legs method
This is the classic method everyone working with soft circuits knows and loves. You simply curl the legs of any long leg electronic component, forming a little ring you can then sew to. I’ve used this method with LEDs, transistors (careful, the legs on transistors break very easily), resistors, photoresistors, and even electrical wire.

Since my conductive thread frays a lot and tends to come loose after a while, I usually finish it up with a drop of wire glue (more about this below).

When I really must use electrical wire, which is the case when working with EL wire, I prefer the stranded kind, which is more flexible that the single-strand. In this case, the first thing to do is twist all the small-gauge wires together and then apply a bit of solder to bond them. After forming the ring, apply some more solder to it in order to get a more solid shape to sew to.

:: The wire glue + snaps method
I’ve often found myself in a situation of having to work with conductive pads, which leaves out the preferred curled legs method. So I made a few experiments and found out that wire glue is perfect for these situations. Unlike conductive ink and conductive epoxy, wire glue is very cheap. It’s also easy to obtain and work with. While wire glue is not particularly good as a glue, it is a very reliable conductor.

Gluing the fabric or thread directly to the pads never really worked for me: it comes off too easily and I haven’t found a good way to reinforce the bond. But metal snaps are just perfect for the job!

Metal snaps on surface mount battery holder

I apply a bit of wire glue to the conductive pad and then, using tweezers, carefully place the male half of the snap on top of it. Just the wire glue wouldn’t be strong enough to keep the snap there once you start snapping and unsnapping your circuit. But, after the wire glue has cured (leave it for a few hours), you can add a couple drops of super glue. This doesn’t affect the conductivity or the connection and ensures a pretty strong bond. Once that’s done, you can just add a strip of conductive fabric to the soft part of your circuit and, using conductive thread, sew the other half of the snap on it.

Metal snaps on board

:: The surface mount + wire rings method
This is very similar to the method described above, except that instead of using snaps you’d strip a piece of electrical wire, make a little ring with it, and solder the ring to the contact pads. This is tricky to do on very small components, such as surface mount LEDs, but not complicated at all with bigger pads.

Wire rings on surface mount battery holder

OSLOOM is is a project led by Margarita Benitez aimed at creating an open source electromechanical thread-controlled loom that will be computer controlled. It will include basic software allowing anyone to simply weave a photo thru a web browser (twill/satin), import weave ready files from other software (such as Bhakti/Alice photoshop method), and then post the software on a repository for others to further develop or customize. In addition, all the loom blueprints will be placed online for anyone to build.

A loom is a device used to weave fabric. The loom itself will be a Jacquard style loom. Jacquard looms allow for the individual control of each thread which in turn allows for photographic imagery to be woven. Jacquard looms like this exist commercially but they are very expensive (upwards of $30,000) which puts them out of reach for individuals and small educational facilities.

The OSLOOM could be produced way more economically than that and truly revolutionize what the studio weaver could accomplish. The idea of a DIY open source loom is one that not only artists could benefit from but many individuals and learning centers could gain a resource by building one of these looms as well.

OSLOOM would have an impact on (but not limited to) the following communities/sectors:
artists
DIY/makers
studio weavers
educational
institutions (large and small)
textile designers
developing countries

This project is inspired by MIT’s FabLab concept and other open source hardware projects such as the RepRap and Fab@Home 3D rapid prototypers and the many DIY CNC projects available already.

Margarita is currently working on making available some cardboard tapestry loom plans for lasercutting. Keep an eye on osloom.org for more information!

PS: I’m already imagining textile circuits weaved with conductive thread/yarn :)

This mitten lights up when its wearer shakes hands with someone. It has two exposed soft contacts around the thumb and across the palm which, when bridged by bare skin, turn on the LED embedded on the flower. The mitten itself was created by fashion designer Isabel Tomás, and we then sewed a simple touch switch circuit onto it using conductive fabric and thread. It also works with high fives and holding hands :)

Isabel and I designed this as a soft circuits exercise for some upcoming materials workshops. Below you can find all the instructions and images we prepared for this purpose.

Note :: The measurements on this tutorial are for very small hands – mine :) Remember to adjust them to your glove size. Also, we used iron-on conductive fabric on our first prototype, but after some wear it started to come off, so we ended up sewing all the conductive fabric to the knitted glove.

:: What you’ll need
Materials
- yarn (or any old glove/mitten, if you don’t want to start from scratch)
- conductive thread
- conductive fabric
- self-adhesive conductive fabric (used on the batteries’ pouch, can be replaced by some non-adhesive, but stiff, conductive fabric)
- fabric or knitted flower
- regular fabric
- regular sewing thread
- 2 metal snaps
- 1 super bright LED
- 1 BC547B transistor
- 2 x 3V lithium coin cell batteries

Tools
- sewing needles
- needle-nose pliers
- scissors

:: Circuit

circuit schematics

:: Knit the mitten

If your knitting skills aren’t as good as Isabel’s you can use any store-bought mitten/glove and skip this step.

:: Add the contacts
On a hand shake the best point of contact usually happens in between the thumb and the index. But we thought it would be fun to also make it work for high fives so we extended the fabric contact strips all the way across the palm.

Cut two strips of conductive fabric approximately 0.5cm (0.2in) wide. One should be around 28cm (11in) long and the other 15cm (6in) – adjust to your glove size.

top side

Cut two vertical slits on the top side of your glove and stitch them so the glove doesn’t come undone. Do the same on the palm side. The distance in between the top and palm slits should be approximately 7cm (2.75in).

palm side

Slide the longer strip of conductive fabric in between the two slits closest to the fingers. On the inside leave an 11cm (4.3) tip on the palm side and 10cm (4in) on the top side. Do the same with the second conductive fabric strip and slide it in between the other two slits, leaving 2cm (1in) on the palm side and 6cm (2.4in) on the top side.

Sew the fabric strips in place.

:: Make the batteries pouch
This double pouch will contain the two 3V coin cell batteries. They should fit very snugly to ensure proper contact.

Cut a piece of non-conductive cotton fabric of approximately 9cm (3.6in) x 6cm (2.4in). Hem the top and bottom on the longest side: one hem should be 1cm (0.4in) high and the other 0.5cm (0.2in). Fold your piece of fabric over itself so that the 1cm (0.4in) hem sticks out. Crease the fold with the iron.

batteries’ pouch :: inside

Next, open your square of fabric and iron on 3 strips of conductive fabric as shown on the image. Use conductive thread to sew on two snap studs at the tip of the 2 parallel strips (on the 1cm/0.4in hem).

Now, fold your piece of fabric back down and, using non-conductive thread, sew the left and right sides of your pouch.

batteries’ pouch :: outside

Turn it right side out and stitch across the middle to make two compartments. The batteries should fit very snugly inside these compartments so make them as tight as possible.

Turn it around so the snaps are facing down, and using a marker write “+” on the right side and “-” on the left.

:: Sew on the top half of the circuit

glove inside out :: top side

With your glove inside out, fold and sew the longer conductive strip as shown above. Using conductive thread, sew a snap socket at the tip of the longest strip of fabric.

Cut another strip of conductive fabric approximately 5cm (2in) long. Place it so the its tip matches the position of the batteries pouch and extends horizontally all the way into the palm side of the glove. Sew it to the glove and attach the second snap socket using conductive thread.

:: Insert the LED

Insert the LED on the flower so that its legs stick out from the bottom. Make sure the legs of the LED aren’t touching each other.

:: Sew on the bottom circuit

glove inside out :: palm side
the LED is represented above as being inside the glove just so you can see where to place it, but in fact it should be embedded on the flower on the exterior, only its legs should extend into the interior.

With the glove inside out, fold and sew the conductive fabric strips as shown above.

Open the legs of the transistor and curl them slightly with needle-nose pliers.

Using conductive thread, sew the emitter of the transistor to the horizontal strip and the base to the vertical strip on the right.

Place the flower on the exterior side of glove so that the shorter leg of the LED (-) is closest to the transistor’s collector and sew them together using conductive thread.

The transistor’s legs break easily, so avoid stretching them too much and add a tiny drop of super glue to the junction area.

Sew the other leg (+) of the LED, with conductive thread, to the left vertical strip of conductive fabric.

:: Make the lining
This is absolutely necessary since it not only makes the glove more comfortable, but also avoids contact between your skin and the exposed circuit (which would cause the LED to be always on).

Use any non-conductive stretchy fabric and sew it to the glove only at the top (near the fingers slit). This will avoid contact between your hand and the circuit while still allowing you access to it.

:: Insert the batteries and attach the pouch
Insert the batteries into the pouch. The one on the right should have + facing up and the one on the left the other way around. Use the snaps to attach the pouch to the glove.

:: Done!
That’s it. Now put your glove on and go shake hands :)

* glove illustrations by Isabel Tomás
** thank you Maurício Martins and Pedro Ângelo

More interesting news from Stanford University’s research on carbon nanotubes, via a Printed Electronics World article:

Ordinary textiles could be transformed into batteries that hold up to three times more energy than a mobile phone battery, by simply dipping them into nanoparticle-infused ink.

Conventional batteries are made by coating metallic foil in a particle slurry and rolling it into compact form – a capital-intensive process. The new energy textiles were manufactured using a simple “dipping and drying” procedure, whereby a strip of fabric is coated with a special ink formula and dehydrated in the oven.

“Wearable electronics represent a developing new class of materials… which allow for many applications and designs previously impossible with traditional electronics technologies,” said the researchers at Stanford University who are developing the batteries and simple capacitors.

The procedure works for manufacturing batteries or supercapacitors, depending on the contents of the ink – oxide particles such as LiCoO2 for batteries; conductive carbon molecules (single-walled carbon nanotubes, or SWNTs) for supercapacitors. Up to now, the team has only used black ink, but Yi Cui, assistant professor of materials science and engineering at Stanford, said it is possible to produce a range of colors by adding different dyes to the carbon nanotubes.

The lightweight, flexible and porous character of natural and synthetic fibers has proven to be an ideal platform for absorbing conductive ink particles, according to postdoctoral scholar Liangbing Hu, who led the energy textile research. That helps explain why treated textiles make such efficient energy storage devices, he said.

Cui’s team had previously developed paper batteries and supercapacitors using a similar process, but the new energy textiles exhibited some clear advantages over their paper predecessors. With a reported energy density of 20 Watt-hours per kilogram, a piece of eTextile weighing 0.3 kilograms (about an ounce, the approximate weight of a T-shirt) could hold up to three times more energy than a cell phone battery.

“The whole thing can be stretchable as well, and extend to more than twice its length,” Hu explained. “You can wash it, put it in all kinds of solvents – it’s very stable.”

They have already received interest from some big-name brands in high performance sportswear and suggest that the military are looking at the possibility of integrating energy textiles into its battle array, a move that could considerably lighten a soldier’s load.

Aside from enhanced energy storage capacity, eTextiles are remarkably durable and can withstand greater mechanical stress.

Potential applications range from health monitoring to moving-display apparel. Scientists at the University of Michigan developed a smart fabric that could be used to power a light emitting diode (LED) by dipping cotton fibres into CNT containing water.

Carbon Nanotube Ink Technology is also being developed for use in other areas. Earlier this month SouthWest NanoTechnologies Inc. (SWeNT), introduced Carbon Nanotube Ink Technology for printing large-area, low-cost devices. Applications include energy-efficient lighting, affordable photovoltaics, improved energy storage and printed electronics.

DuPont and Cornell University presented last year a new and relatively simple process to separate metallic and semiconducting carbon nanotubes into a high-performance CNT ‘ink’ that solely contains semiconducting tubes. Funded by the U.S. Air Force this could prove promising for printed, thin and flexible electronics for TFTs and Photovoltaics.

(via clothbot)

Pa++tern, created by Daito Manabe + Motoi Ishibashi, is a combination of an installation and an esoteric programming language for embroidery in which a series of industrial sewing machines are controlled by twiterers. Here’s the process: using a simple environment, users create a short program for an embroidery pattern and send it over to the machines through twitter, which in turn embroider it on an actual t-shirt (you have to acquire the t-shirt). Check it out here.

(via Kerrin Mansfiled – thanks Kerrin!)