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This video has been graciously sponsored by Dollar Shave Club. If you want to improve your shaving routine and support my channel at the same time you should pick up their amazing starter kit for just 5 dollars by going to Indigo’s one of the oldest dyes used for textiles and it’s been around for thousands of years. For most of this time though, it was derived from plant sources which was both costly and not very efficient. This made it quite rare and it was often reserved just for luxury products. Plants remained the main source of indigo all the way until the late 1800s when it was successfully synthesized. The German chemist Adolf Von Baeyer first synthesized it from isatin in 1878 and then from 2- nitrobenzaldehyde in the early 1880s. This second synthesis was very easy to do in the lab on a small scale, but it wasn’t ideal for industrial production. By the turn of the 1900s though, the first commercially viable method was developed by Pfleger. It started with aniline, which is a readily available and cheap starting material. This process has been refined over time and a variation of it is currently the major way that indigo is synthesized. With that being said, I’m gonna be doing the easier method that was developed by Baeyer. Then I’ll use the indigo that I make to dye some socks and a pair of jeans. I’m also gonna keep some of the indigo so that I can make indigo carmine. Unlike regular indigo, indigo carmine is water-soluble and it’s commonly used as a food colorant. Okay, so these are all the ingredients that I used to make the indigo. From left to right, we have diethyl ether, 2-nitrobenzaldehyde, sodium hydroxide, acetone, and ethanol. The diethyl ether and the 2-nitrobenzaldehyde had to be purchased online, but I was able to get everything else locally. To start things off, I added 5g of sodium hydroxide drain cleaner, and then I topped it off with water just up until the 125 mL mark. Then I turned on the stirring and I waited for everything to dissolve. A few minutes later, I had a nice and clear solution, and for the time being I place it on the side. In another larger beaker, I added 25 g of the 2-nitrobenzaldehyde, followed by 250 mL of acetone. I turned on the stirring, and when everything dissolved I slowly added an equal volume of water. The 2-nitrobenzaldehyde isn’t very soluble in water, so as it was added some of it precipitated out and caused the solution to become cloudy. This was totally fine though, and it was expected to happen. Okay, so now that I had both these solutions prepared I was ready for the actual reaction. I went and got my sodium hydroxide solution from earlier and I just slowly poured it into this one. I started by adding just a very small amount and the color quickly changed. This reaction is formally known as the Baeyer-Drewsen Indigo Synthesis and it’s classified as a type of aldol condensation. Two molecules of 2-nitrobenzaldehyde combined with two molecules of acetone to form the final indigo. Indigo is practically insoluble in water, so it fell out of solution as it formed. The reaction is exothermic so it heated up a bit and you can see acetone vapors condensing on the walls. When I was done adding all the acetone, I put it in an ice bath and I let it stir here for about 15 minutes. I then moved on to filtering off all the indigo. In my case I chose to do a vacuum filtration just because it’s a lot faster, but I also could have done a gravity filtration through something like coffee filters. After everything’s been pulled through, the indigo is washed with a small amount of distilled water. I turn on the pump to get rid of the water and then I wash it again, but this time I use 95% ethanol. Using the stir rod I really try to mix everything up and break apart any large chunks. This step helps get rid of some impurities inside products, but it also really helps to pull out the water and dry up the indigo. Now, there’s just one last washing to do, and this is with diethyl ether. So just like before I add a small amount, mix it thoroughly, and then pull it through. Diethyl ether is extremely volatile, so to get rid of most of it I just need to leave the pump on for several minutes. At this point it is quite dry, but there’s still a bit of solvent left over. To get rid of the last bit of it I just need to leave this out for a day or so. I weighed it out when it was all dry and I got a mass of about 11 g This process of making indigo isn’t the most efficient so the percent yield here is only about 51% Anyway, now it’s time to actually use the indigo. Before trying it on my good pair of white jeans or my socks, I’m gonna do it on a small scale and I’ll also explain to you guys exactly what’s going on. The first thing I needed to do was make the dye bath. So to a beaker I added 40 mL of water followed by 0.8 g of sodium hydroxide and I turned on the stirring. When the solution was completely clear, I added 0.2 g of indigo, which was practically insoluble Then on top of this, I dumped in 0.3 g of sodium dithionite, turned on the hot plate, and brought the mixture to a boil. The major reaction that was going on here was the reduction of indigo to leuco-indigo, where sodium dithionite was acting as the reducing agent. Unlike the oxidized indigo that I started with, leuco-indigo is much more soluble in water and it’s actually colourless. As the reaction progressed, it was supposed to slowly clear up. However, even after I boiled it for a couple minutes there was still a bunch of indigo so I added some more sodium dithionite The indigo quickly started to disappear and I was eventually left with a dark yellow-orange solution. As far as I know, the orange color isn’t coming from the indigo and it’s coming from the reaction between the sodium hydroxide and the sodium dithionite. At this point I turned off the hot plate and I was ready to dye something. I just used the small piece that I cut out of a sock. I squished it down but it was having trouble sitting below the surface of the water, so I added some more. I mixed it around a bit and then I just let it sit here for about ten minutes. When I came back I took off the cover and I pulled out the sock piece. In the solution it was a yellow-orange color but the moment that it was removed it started to change. And by the time that I took away the beaker and put it on a paper towel it had already started turning blue. The reason this happens is that because once it’s removed it comes into contact with oxygen in the air. The oxygen first oxidizes any reducing agent that might remain and then it starts oxidizing the leuco indigo back into the insoluble blue form. This technique of first soaking the fiber in the soluble reduced form of the dye and then converting it back to the insoluble one is generally known as vat dyeing. There are many different dyes that can use this technique, but indigo is probably the most famous one. In another video I did on azo-dyes, I pre-soaked a sock in one solution and then I directly synthesized the insoluble dye in the material. Although the details, chemicals, and exact technique for that one is quite different, the general idea is actually pretty similar. The material is first soaked with some soluble form of the dye and then it’s converted to its insoluble form which gets trapped inside the fibers. Anyway, now that I know it works well, I’m gonna go ahead and dye some clothing starting with the pants. However, pants are way too big for a beaker so this time I’ll be doing it in a two gallon bucket. The stock dye solution still needs to be made in a beaker though. The recipe for this run is a bit different than the last one but the general idea is the same. I added 6 g of sodium hydroxide to 200 mL of water and waited for it all to dissolve. Then I added 6 g of sodium dithionite and when that all dissolved I dumped in 5 g of indigo. The top was covered to protect it from oxygen and I turned on the heating. Like before, I boiled it for a couple of minutes but it didn’t clear up, so I started to add small amounts of sodium dithionite. After one of the additions though, the whole thing quickly turned orange, and there was a bunch of precipitate. I transferred everything to a large beaker and topped it off to about 500 mL but it didn’t seem to do anything. The precipitate looked yellow which I figured was sulphur, which might have formed because I
messed up the sodium dithionite and sodium hydroxide balance with all my additions. So to try to fix this I added more sodium hydroxide, which should react with any sulphur and convert it to soluble sodium sulfide and other polysulfides. This caused the solution to quickly clear up and after boiling it for a couple minutes, all of the precipitate completely disappeared. I’m not exactly sure why in both runs I needed more sodium dithionite than the recipe asked for. I think it’s because my sodium dithionite is just old and not very good, but it also might be just because I’m not very patient and didn’t let it boil for long enough. Also, i think the solution is red this time instead of the yellow-orange that we had last time just because the concentration of polysulfides is way higher. In any case, the solution was done so i took it off the hot plate. While I was initially waiting for the dye solution to come to a boil, I prepared the vat. I filled it with 5 L of water and Dissolved in 1 g of sodium dithionite and 1 g of sodium hydroxide drain cleaner. This was just done as a pretreatment to try to remove any oxygen from the water. When the dye stock was ready I just poured it in. It’s important to do this carefully though to prevent splashing and from introducing more oxygen to the vat. I mixed it around a bit and very quickly it looked like it was all turning green or blue. This was just the surface layer though because it was reacting with oxygen in the air The vat was now ready so I slowly dipped in the pants. Then using my glass mixer I squished them down to thoroughly wet everything and to try to knock out any, air bubbles When I felt I’d done a decent enough job, I covered the top and let it soak for about 15 minutes. 15 minutes later I take out the pants and squeeze out as much liquid as possible. With small articles it’s best to do this under the surface of the liquid, because squeezing it out above like this will introduce quite a bit of oxygen. I spread them out and i let this side oxidize for about eight minutes, and then I flip them over to expose the other side for another eight minutes. I was originally planning to just do one dye run but I ended up putting it back into the vat for another 15 minutes and repeating the oxidation. Every time this is repeated the fibers will get a stronger color and commercially, with indigo, dyeing cycles are often done several times. When they were done I squeezed out as much excess liquid as I could and then I left them out for 24 hours. While they were wet, they had the classic indigo jeans color but as they dried they lightened up quite a bit. I then wash them twice using soapy water and let them air dry for another 24 hours The final result, was in my opinion, a really cool looking pair of pants. If you look at them closely, though, you can see that the color isn’t even. This is mostly because of wrinkles and air pockets in the pants during the dyeing process which prevents the indigo from being applied uniformly. I think the subtle effect is cool but many cultures, for example the Japanese, have turned this into an art of its own. In Japanese it’s referred to as shibori, but in the west it’s more commonly known as tie-dye. The cloth is folded, tied, or packed in very specific ways to produce interesting and intricate patterns. In general, blocking dyes from penetrating a certain area of a fabric is known as resist dyeing. Besides the Japanese methods, there were many other ways to do this. For example, by first treating the cloth either starch paste or wax. In the textile industry, they generally don’t have this problem of uneven colors because they first dye the fiber feedstock and then make the clothing. Another major reason to dye the fibers beforehand is to get stronger, more vibrant colors The final clothing, especially with things like denim, can be quite densely packed, which prevents the dye from penetrating very efficiently. I think this, along with the fact that I didn’t cycle my pants several times is the reason why they’re a light blue instead of the dark blue that jeans are normally associated with. Anyway, just for fun I also decided to dye some socks. I just threw four pairs into the vat and used the same process as the pants. I left them in for 15 minutes, let them oxidize for another 15, and then repeated the process. They were washed thoroughly with soap and water and left out to dry. This was the final result, and just like the pants, I thought they looked pretty good. Just the quick thing that I wanted to mention was that if you wanted to try this you don’t have to make the indigo yourself and you can just buy a tie-dye indigo kit from somewhere like Amazon. The process used by the kits is also a bit easier than what I did because the indigo is pre-reduced. If you’re interested in checking it out, there’s a kit on for just $10 and I’ve put a link in the description. I’m gonna be keeping one pair for myself, but I’ll be giving away the other three, along with some NileRed beaker mugs. Before I talk about the details of the giveaway though, I’m just gonna give a quick shout out to Dollar Shave Club, which is the sponsor of this video. For only $5 with free shipping you can pick up their starter kit using my personalized link in the description. This kit includes their really high-quality executive aluminum handle, several razors, body cleanser and shave butter, and some One Wipe Charlie butt wipes. And after that extra razors are only a few bucks a month. Razors in stores tend to be quite expensive, so for a lot of people the best part about dollar shave club is the really affordable price. For me, though, it’s the fact that the razors are just delivered and I don’t have to remember to go and pick some up. I’m really forgetful and i constantly forget to do basic things so before I discovered Dollar Shave Club, it was not uncommon for me to run out of razors and just use the old, dull, and rusty one for a couple weeks. What’s also nice, is that if you don’t shave often or if you’re like me and don’t really have much to shave, you can change your option to every other month or even skip a month if you still have fresh razors. So if you want to support my channel and simplify your life at the same time you can pick up a kit of your own by going to Or, you can also just click the link in description. Okay, so for the giveaway, what’s at stake are three kits, where each one has a pair of socks and a NileRed beaker mug. If you want to participate you can follow the link in the description and all you need to do to enter is subscribe to me on YouTube, follow me on Twitter, or visit my Instagram page. It doesn’t matter what country you’re from, because I’ll ship it anywhere in the world absolutely free, and I’ll also pay any duties or fees if you happen to be charged. I’ll let the contest run for a week, and then I’ll directly contact the winners. As usual, a big thanks goes out to all my supporters on Patreon. Everyone who supports me can see my videos at least 24 hours before I post them to YouTube. Everyone can directly message me and anyone who supports me with $5 or more will get their name at the end like you see here. [OUTRO]

James Carver

18 Replies to “Making Indigo – The dye that makes jeans blue”

  1. In Biblical times, the purple (Tyrian Red) dye reserved for royalty was obtained from the Murex snail. This same dye, when exposed to sunlight, produces indigo blue, which is the color that the God of Abraham commanded Israel to weave into their garments and tassels at the 4 corners of their clothing (tsitsiot).

  2. Years ago I was on an exchange program in Germany and at one point toured a BASF indigo facility. The indigo color permeated everything… forklifts… vehicles… buildings… It was really quite surreal.

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