Sciencemadness Discussion Board

Making ultramarine

Arcaeca - 26-9-2019 at 21:23

It me, the pigment guy

It occurred to me that since I have sulfur powder laying around from when I was going to try to use it to make CaS (until I found out that it's easier to just reduce CaSO4 by burning it with C in a crucible), I might as well try to use it to make ultramarine. The procedure listed by Wikipedia requires powdered sulfur, powdered charcoal, sodium carbonate, sodium sulfate and iron-free kaolin, although I know HTME has made it before without (as far as I know) the sodium sulfate. You mix them all together (100 parts kaolin, 100 parts sodium carbonate, 60 parts powdered sulfur and 12 parts charcoal, according to and then heat the living crap out of it, at least 750 C, for several hours.

I have powdered charcoal and powdered sulfur; I have calcium carbonate (chalk) but opted to use some charcoal/wood ash which I gather is probably mostly sodium or potassium carbonate. The problem is the kaolin; I've purified clay from my backyard before by filtering most of the dirt/sand/twigs out of it, so I have clay on hand (even dried clay that I can grind up), but I'm fairly sure it's not kaolin - if for no other reason than it has a reddish-brownish tinge to it that pure kaolin does not.

But when I did grind it up into a powder and put all 4 of these things tightly packed in a 6 oz graphite crucible - covered with a rock for half that time as a makeshift cover to approximate anaerobic conditions - and heated with a blowtorch for 3 hours, the result was... grey. Maybe a slight bluish undertone, but not blue.

Anyone know how pure the ingredients have to be to get a good result?

phlogiston - 26-9-2019 at 23:45

Wood ash is not mostly sodium or potassium carbonate. I've extracted potash and fund the yield pretty low for a given volume of ash. Most of the volume at least is something else. I suspect it is mostly silica.

Wikipedia specifically states that the clay used is to be iron-free. No reference given though.
If your clay is not white, iron is very likely among the impurities.

Are you limiting yourself to use only materials you can source yourself from nature or with no extra budget, or would buying some pure kaolin and soda be allowable?
They are not expensive and that would be the first I'd try.

[Edited on 27-9-2019 by phlogiston]

rockyit98 - 27-9-2019 at 03:09

fire brick are made from aluminium silicate which is kaolin.maybe check local pottery store they must have kaolin . sodium carbonate can by from a supermarket as baking soda (sodium bicarbonate),also Potassium sodium tartrate ( Rochelle salt) will decompose into sodium and potassium carbonate.sodium sulfate can get from adding baking soda to Epsom salt.

you can get "kaolin" from clay by heating it with molten NaOH and adding water after the mix cool down.filtering the sodium silicates and Aluminate and leaving it to absorb CO2 from air.

fusso - 27-9-2019 at 04:37

But wheres the blue colour?

12thealchemist - 27-9-2019 at 09:09

Quote: Originally posted by fusso  
But wheres the blue colour?

From wikipedia:


The pigment consists primarily of a zeolite-based mineral containing small amounts of polysulfides. It occurs in nature as a proximate component of lapis lazuli containing a blue cubic mineral called lazurite. ...... The major component of lazurite is a complex sulfur-containing sodium-silicate (Na8–10Al6Si6O24S2–4), which makes ultramarine the most complex of all mineral pigments. Some chloride is often present in the crystal lattice as well. The blue color of the pigment is due to the S3−• radical anion, which contains an unpaired electron.

Arcaeca - 27-9-2019 at 11:59

Quote: Originally posted by phlogiston  
Are you limiting yourself to use only materials you can source yourself from nature or with no extra budget, or would buying some pure kaolin and soda be allowable?

Best way I know how to explain it is that I'm limiting myself to materials that are easy enough to source that:

  1. I don't have to order them from a chemical supplier (but can get them from e.g. a hardware or grocery store), and
  2. that people in, say, 300 BC would've had access to - so either straight from nature or 1 or 2 steps removed and not requiring any fully synthetic chemicals that have only been made available by the Industrial Revolution

So obviously kaolin and soda ash fulfill both criteria; it's just that if I can make it work with what I already have on hand, I might as well try, instead of spending more money that i don't have to.

Quote: Originally posted by rockyit98  
you can get "kaolin" from clay by heating it with molten NaOH and adding water after the mix cool down.filtering the sodium silicates and Aluminate and leaving it to absorb CO2 from air.

How much NaOH for how much ground clay? The clay doesn't sinter during the process dos it? And is the CO2 just supposed to make carbonic acid in the water to neutralize the NaOH? If so can you speed up the process with e.g. HCl?

I'm having trouble finding a pottery supply store nearby to buy kaolin from, which is why I'm looking at making it myself.

rockyit98 - 27-9-2019 at 20:49

Quote: Originally posted by Arcaeca  

How much NaOH for how much ground clay? The clay doesn't sinter during the process dos it? And is the CO2 just supposed to make carbonic acid in the water to neutralize the NaOH? If so can you speed up the process with e.g. HCl?

Precious Metal Refining & Recovery, Episode 16: Aluminum From Dirt


Arcaeca - 28-9-2019 at 19:37

So I went to the nearest wholesale pottery supply store I know of that sells dry powdered kaplin and picked up 10 lbs of it. Then I tried redoing the procedure with kaolin instead of my backyard clay, and chalk powder instead of wood ash which should hopefully be a better source of carbonate. The propane tank was running low around the 3 hour mark the blowtorch went out, so I think the heat output was just never high enough for the crucible to get up to the required temperature. The result was pretty much the same grey as last time.

So then I swapped out the propane tank for a new, full one and retried for a 4th time with the same kaolin/chalk/sulfur/charcoal mixture. With the blowtorch on almost full blast, aimed at the bottom of the crucible, covered, for 4.5 hours. And it's still just grey.

I can't think of anything else I can even do. Buy actual sodium carbonate instead of trying to sub in calcium carbonate (as chalk)? But I can't imagine why that would make a difference. Is it still just not getting hot enough - do I need an actual kiln?

Attached: on the left, the darker grey powder produced after 4.5 hours of firing; on the right, the light, unfired powder.

IMG_4847.JPG - 1.7MB

[Edited on 9-29-2019 by Arcaeca]

Metacelsus - 29-9-2019 at 04:52

Quote: Originally posted by Arcaeca  
chalk powder instead of wood ash which should hopefully be a better source of carbonate.

What kind of chalk did you use? Blackboard chalk is calcium sulfate.

And I think that actual sodium carbonate would be necessary. You could use washing soda, or heat baking soda until it decomposes.

rockyit98 - 29-9-2019 at 06:28


OMG where to begin,you just can't mix some ingredients together and heat it in a ghetto setup and hope it would be fine.ultramarine is one of the most complex inorganic pigment out there (Na8–10Al6Si6O24S2–4) you need to invest in electric kiln. it not that hard to build one yourself. i'm sure there is number of post and YT videos that tell you how.maybe less than 100$.over time you will save much more money because efficiency and electricity been ,much cheaper. i build mine that can get up to 1100C for just under 50$ with PID and 25L capacity. you really need Na2CO3, chalk powder wouldn't cut it. find a patent or scientific a paper that goes over the process.

unionised - 29-9-2019 at 07:46

Quote: Originally posted by rockyit98  

you need to invest in electric kiln.

Just like they did in 1814.

Arcaeca - 29-9-2019 at 08:33

Quote: Originally posted by Metacelsus  

What kind of chalk did you use? Blackboard chalk is calcium sulfate.


Arcaeca - 29-9-2019 at 15:45

You know, I just realized that sodium is actually incorporated into the structure of ultramarine. I thought using chalk would be fine because the sodium carbonate is only needed for the carbonate ion, but in fact I do need the sodium after all. Oops.

So I put a bunch of baking soda on a baking sheet and put it in the oven at 200 degrees Fahrenheit for a little over an hour to decompose it to sodium carbonate. Then I repeated the previous procedure with this sodium carbonate instead of chalk - mix with kaolin, sulfur and charcoal, tightly pack into a crucible, heat with a blowtorch (about a centimeter and a half from the base of the crucible) for 3 hours and then uncover... and...'s darker, but no bluer.

I can't think of anything else I could've done, other than if the crucible simply isn't getting hot enough. But I simply can't afford a box furnace like ideally you'd want to use, which run several hundred USD. Another blowtorch would only put me out another $20 or so, but something tells me even 2 blowtorches aimed at the crucible still won't give me blue.

IMG_4859.JPG - 2.5MB

MrHomeScientist - 30-9-2019 at 05:51

Two torches would help it heat up faster, but may not ultimately get it any hotter. You should try some sort of insulation. My first "furnace" was made of six hard firebricks: one for the floor, one for the lid, and four on their sides as walls. Nothing mortared together at all. The only labor needed was to drill a hole in the bottom brick for the torch burner. That helps a lot, and is very inexpensive. Plenty of room for improvement, obviously, but it might give you that extra little push that you need.

unionised - 30-9-2019 at 13:18

Is it just me who thinks this synthesis- while well documented- is as fishy as Grimsby?
While the mix is on the way to 750C it goes through the boiling point of sulphur and into the range where any sulphur that's left would react with carbon to form the very volatile CS2.
At best, I'd try putting the sulphur at the bottom and a "lid" of Na2CO3 on top to try to keep the stuff all in the same place.

Arcaeca - 30-9-2019 at 21:40

Quote: Originally posted by unionised  
At best, I'd try putting the sulphur at the bottom and a "lid" of Na2CO3 on top to try to keep the stuff all in the same place.

I'm fairy sure the mixture has to be well-mixed, but I'm sure it wouldn't hurt to put a little extra sodium carbonate on top.

Anyway, I bought a bunch of bricks and pavers (not firebricks... just regular bricks) and a 3/8" masonry drill bit to make a makeshift kiln; general set up looks like this but I'm not actually going to fire anything in it until I get my hands on some gloves that can handle the heat.

IMG_4864.JPG - 2MB

kiln.png - 24kB

[Edited on 10-1-2019 by Arcaeca]

MrHomeScientist - 1-10-2019 at 06:29

Nice! I'm interested to see if that helps you.

One word of caution, though: since those aren't firebricks, they aren't meant for high heat (obviously). I'd advise heating them slowly (if possible) to bake out any moisture. Pockets of moisture can flash boil and crack the brick or even make little explosions that send brick shrapnel flying. It might be worth firing it first with nothing in it, just to make sure it holds up.

I know this is just a quick thing that you don't want to spend a lot of money on, but I thought I'd post some tips on furnace design in case you want to incorporate that down the line. Metalcasting is one of my other hobbies, so I've acquired a lot of information on furnaces!

Here's a good design that I use, from "The Hobbyist's Guide to Casting Metal, 2nd Edition":

Furnace Design, book.JPG - 391kB

The important points:

Of course, this is all in an ideal world where you have infinite time and budget. Like I said, my first furnace didn't have any of this and it worked just fine. My only concern with your current setup is that the bricks aren't meant for heat, and could fail. I'd test it first, and make sure they're completely moisture-free by pre-heating them.

Arcaeca - 1-10-2019 at 10:25

My design includes air intakes because the nozzle of the propane torch would be physically inside the kiln, not right below a hole in the bottom. The edgestones I'm using for the base aren't quite tall enough to give the torch that much clearance. So the propane would have to ignite using the oxygen actually in the kiln itself, not directly below the kiln, and that's going to run out quickly if it doesn't have some way of being replenished. Or so my thought process goes.

Thinking of also picking up a tube of firebrick fireplace mortar to coat the insides to reduce the rate of heat loss to the brick walls themselves; the stuff I'm looking at is rated for up to 2000 F.

wg48temp9 - 1-10-2019 at 13:23

Yes you have to use dry bricks and heat slowly at first.

The grey blocks look like they are cement blocks so they will crumble and crack as the cement dehydrates.

I would mount the crucible as is described in the procedure in hole in the top of the furnace. That may be important to reduce the combustion gasses getting in to the crucible when the lid is removed.

I wounder if the reaction mixture could be heated in a microwave oven as it contains carbon and ionic salts.

Arcaeca - 13-10-2019 at 14:20

Okay, so almost 2 weeks later, after building the kiln, mortaring up all the holes that the heat would've escaped through, curing the mortar, drilling an exhaust hole in the top and 2 air intake holes in the bottom, setting up some cardboard ducts and using them to push air into the firing chamber with a fan, and buying some fiberglass gloves rated for 2000 degrees Fahrenheit, I fired up the kiln.

The ultramarine powder is still just dark grey.

I have no idea what else could be wrong besides just simply still not getting hot enough (target temperature is, what, like 1400 F?). Only other thing I can think of is to just pump way more propane and way more air in, e.g. with a stronger fan and a hooking the blowtorch up to a 20 lb propane tank instead of a 1 lb canister, which would require a converter.

Or I could scrap the combustion altogether and try to heat it with wires? But the wires would have to get so hot they'd melt themselves before getting the crucible up to the target temperature.

Twospoons - 13-10-2019 at 17:47

From Wikipedia:


The preparation is typically made in steps: The first part of the process takes place at 700 to 750 °C in a closed furnace, so that sulfur, carbon and organic substances give reducing conditions. This yields a yellow-green product sometimes used as a pigment. In the second step, air or sulfur dioxide at 350 to 450 °C is used to oxidise sulfide in the intermediate product to S2 and Sn chromophore molecules, resulting in the blue (or purple, pink or red) pigment.[8]

Could it be you are not getting enough air to the mix in the second step? If you are using an enclosed "kiln" arrangement with a gas flame, there may be very little oxygen available.

For the second step maybe you could replace the gas flame with a hot air gun - my one can reach 600C, which is plenty hot enough.

WGTR - 13-10-2019 at 19:57

Sodium carbonate and sodium sulfate melt around 800-900C.

Na2CO3-Na2SO4.jpg - 71kB

Adding sodium to a clay fluxes it (and lowers its firing temperature). I suspect that the process may result in a fairly coherent mass if fired to about 750C for an hour or two.

The stated yield is rather low (1-3g) in the documentation, and the experimenter is directed to carefully pick through the product and select the appropriately-colored parts for further processing. I do not know if the product is supposed to be located in the hottest area of the crucible, near the top, or where exactly. It is also possible that the heating-time/results depend on how tightly the crucible lid fits during the initial firing.

I have attached an interesting document regarding the reduction from sulfate to sulfide in a sodium carbonate/sulfate melt, when mixed with charcoal. It might help explain a bit more about what is going on. Have fun!

Attachment: cameron1983.pdf (1MB)
This file has been downloaded 247 times

Arcaeca - 12-12-2019 at 20:50


Okay, so I dug a big hole and built a makeshift draft furnace out of brick, and then filled it up with as much charcoal as I had on hand. That was enough to fill it up about 1/3 of the way, so I kept having to add sticks faster than the furnace could burn them. The natural draft wasn't a good enough oxygen supply to keep the charcoal burning, so I forced air in my taking the fan in my bedroom and aiming it straight at the opening at the bottom of the furnace.


It's no longer completely grey. Definitely some blue in there! I mean, not much, but it's an improvement.

I'll try it again tomorrow with a better fuel supply and see what that gets me.

ultramarine.jpg - 2.3MB

Metacelsus - 13-12-2019 at 15:13

Looks interesting, please keep us updated. Is there any practical way for you to measure to the temperature in there?

G-Coupled - 13-12-2019 at 21:27

Hey, that's looking better! :cool:

Maybe you would have more joy with an electrically powered furnace using NiChrome resistance wire or similar? The designs are pretty simple, even with a basic working knowledge of electronics.

Arcaeca - 14-12-2019 at 11:42

I don't have a practical way to measure the temperature. I mean, a pyrometer would be the most obvious solution, but I don't have a pyrometer.

I was thinking of building an electric furnace (since they tend to cost $2000 if you buy them), and I found a tutorial for doing so, but since I have no experience building anything electrical, I tried asking around for advice (stuff like "attach alligator clips to the heating element wire, connect alligator clips to the controller, connect controller to a surge protector, connect surge protector to the outlet, right?" and "does DC vs. AC matter if I just want to get a wire hot (and if not, would my 30V 10A DC power supply work)) - but nobody gave me any useful answers and just kept telling me not to do it. So I eventually gave up on it.

Anyway, the better fuel supply got the furnace so hot that:

  1. the bricks the furnace is made of are falling apart
  2. one crucible cracked and its lid shattered
  3. the water bath I put on top - to heat up a mixture of copper(II) sulfate and sodium metabisulfite to boiling, to make Chevreul's salt - got so hot that it literally smelted the Chevreul's salt and deposited a chunk of copper on the bottom of the vessel that I can't get out

I believe this is what we in the business refer to as "suffering from success".

Anyway, this last run was a catastrophic failure. I did two crucibles at once; one I spilled 90% of its contents while trying to retrieve it from the furnace, but what I had left had no trace of blue. The other one - the cracked one with the broken lid - had no blue either.

Why is ultramarine so hard to make what the hell

G-Coupled - 15-12-2019 at 00:31

Sounds like you're on your way to sucess. Keep at it!

It's not too hard at all to build an electrical heater - you're just shoving current down a resistance wire at the end of the day. So long as you've wound an amount of suitable gauge wire that's in the right ballpark in length and know its resistance, you can quite easily calculate what's needed.

A simple thermocouple would be sufficient to measure the temperature, or you could invest in an inexpensive IR thermometer.

[Edited on 15-12-2019 by G-Coupled]

Arcaeca - 15-12-2019 at 13:44

I tried again with both crucibles, including the cracked one. I put a couple pieces of brick that chipped off the interior walls of the furnace in top of the crucible as a crude, loose-fitting lid and hoped for the best. It doesn't seem to have mattered and may have even helped, because the yield of useably-large blue pieces was larger than ever before. I also left the top of the furnace uncovered, which may have somehow affected it; the fire also nearly went out at one point (from what I can tell, because some non-flammable rubble blocked much of the oxygen intake) and had to be re-ignited, which resulted in some temperature swings that may also have affected it.

The yields was still not uniformly blue, but as said before, more blue was recovered than ever before. However, one crucible had a sort of greyish-blue-green, like a mix of charcoal and teal, vs. a nicer royal blue obtained from the other crucible (the cracked one without a proper lid).

There was a large variation of color within the crucibles. Certainly lots of offwhites, pale oranges and dark greys from where it didn't get hot enough, but also greens and especially reds. There were a couple large pieces with an almost ruby-red inset (color not captured well by the camera) surrounded by white that sort of reminded me of cinnabar.

Overall it seems the yield is rather fickle, both in quantity and quality of blue color. If I had more control over the reaction conditions, as in an electric kiln, I might try and play around and see what the optimal firing temperature is and whether the lid makes a big difference or not. For now though I think I just don't have enough control over the conditions to say one way or the other.

IMG_5491.JPG - 2.2MBIMG_5492.JPG - 2.2MBIMG_5494.JPG - 3.2MB

rockyit98 - 15-12-2019 at 15:50

HTME The Joy of Painting From Scratch
"how to make ultramarine"

Arcaeca - 15-12-2019 at 16:51

Yeah, that video is what gave me the idea to start making pigments in the first place; I saw it basically right when it was released. The problem is he doesn't say how much of any ingredient to use (although it looks like he's using a whole lot more charcoal powder than I am, since my unfired powder is off-white and his is grey).

[Edited on 12-16-2019 by Arcaeca]

wg48temp9 - 16-12-2019 at 09:00

Below is a link to procedures recipes and discussion about the synthesis.

Its got a chromaticity diagram showing the colour range for different procedures.


ultra-crom.JPG - 59kB

Just in case the link decays below is the file:
Attachment: ultramarine-synth-hamerton2013.pdf (664kB)
This file has been downloaded 164 times

[Edited on 12/16/2019 by wg48temp9]