Talk:Realgar

Orpiment is not realgar

I have removed the following text

Mixed with two parts of slaked lime, orpiment is still very commonly used in rural India as a depilatory. It is also used in tanning industry to remove hair from hides.

and placed an edited version in the entry for orpiment.--King Hildebrand 14:01, 15 July 2006 (UTC)

I have expanded the brief mention of the pyrotechnic uses of realgar, and clarified the obsolesence of a previously mentioned use.Bert2368 05:31, 27 October 2007 (UTC)

Sandarac

Was realgar made from the sandarac tree's resin?--عبد المؤمن (talk) 20:06, 30 August 2018 (UTC)

No. While the mineral realgar (red arsenic sulphide) and later red lead as well were called "sandarach" in the past, the plant resin was sometimes distinguished as Arabian Sandarach. NRPanikker (talk) 01:28, 31 March 2019 (UTC)

To add to the "Occurrence" section

If it's found in China, Peru, and the Philippines, why not add a mention of that to the "Occurrence" section? 173.88.246.138 (talk) 22:17, 3 May 2022 (UTC)

Reference for "repel snakes" comment

The article states "it was sprinkled around houses to repel snakes and insects, as well as being used in Chinese medicine.[13]"

There is only two occurrences of the word "snake" in the reference [13] and both instances reference the use of Orpiment for snake bites. Only one occurrence of "insect" is present referring to the use of Orpiment for insect stings. Nowhere can I find any reference to sprinkling Realgar around to repel snakes and insects. Perhaps the reference [13] is for the Chinese medicine comment and not the the sprinkling comment, in which case there should be a reference for that comment. It is quite a fundamental claim to claim that there is a written record of Realgar being used as an insecticide or insect repellent, so this would be very interesting. — Preceding unsigned comment added by 134.65.154.51 (talk) 14:05, 6 December 2022 (UTC)

I removed the snakes part. Most of the "uses" section is suspect in my opinion. Realgar is so insoluble that even its toxicity is questionable. Bottom line: realgar is a minor ore of As, its pretty, and that's all there is.--Smokefoot (talk) 16:32, 6 December 2022 (UTC)

Why does As4S4 Link here?

So As2S3 and Orpiment are separate pages like it should be, since the mineral pages get into a quagmire of mineralogy stuff chemists don't generally care about and the chemistry pages do the same with chemistry stuff that mineralogists don't care about, plus they're just different topics really... there's also the issue of the infoboxes, which contain very different info... is this just because nobody has made a page for As4S4 yet or is there a redirect screwed up somewhere? A Shortfall Of Gravitas (talk) 06:25, 26 September 2025 (UTC)

I dont think that anyone cares. I mean, there just aren't many people dedicated to As chem, except environmentalists who worry about groundwater etc. Also As2S3 is pretty easy to generate (see qualitative inorganic analysis) from H2S + many As compounds, whereas I dont think that As4S4 is readily synthesized. Being molecular, As4S4 a much more interesting species in my opinion, not that that matters. The comparison with S4N4 is thought provoking. Not sure if the analogous P4S4 is known.--Smokefoot (talk) 13:02, 26 September 2025 (UTC)

Brauer lists As₄S₄ synthesis from the sorta obvious direct fusion of equimolar parts of the elements in nitrogen, in a thick-walled, sealed tube, then purified by vacuum sublimation. The less obvious part is the heat, 500–600 °C. I'd think you'd want it below the boiling point of realgar The tube material wasn't specified but sulfur doesn't react with most transition metals until higher temps than that are reached so it may not be overly important. While not as easy to make as As₂S₃ I'd personally rather deal with the As₄S₄ synth than have to crack open an H₂S cylinder for the standard orpiment synths (or worse, generate it). Simply using H₂S isn't nearly as bad as lots of the synths in Brauer, but I also wonder how many graduate assistants some of the chemists who wrote them up killed off in the process of getting each synth working... although more likely they were performing them while smoking cigarettes and just left the room if they tasted anything wrong as was the style at the time.

P₄S₄ apparently does exist, and in roughly the same crystal geometry and with more or less identically structured alpha and beta forms as realgar. I couldn't find much info about it as it isn't commercially important. Tetraselenium tetranitride (Se₄N₄) is also a thing, and even more sensitive an explosive than S₄N₄. If the tellurium equivalent can exist for any length of time, I can't find any info about anyone making it. People aren't exactly lining up to do tellurium chemistry in the first place, probably less so when the compound would almost certainly detonate on any attempt to isolate it for study or get a crystal structure. The tetraarsenic tetranitride doesn't appear to have been made, the closest thing is polymeric (As₁₀N₁₀)_n.

I'm mainly interested from the perspective of pyrotechnics, and even that is mostly historical, but it has several odd qualities in that realm.

One strange aspect is that its sensitivity to friction and impact when mixed with chlorates is abnormally high, far more so than antimony trisulfide (which is more sensitive than sulfur / chlorate mixtures though not unstable like that mixture is), more in the direction of the fundamentally unsafe red phosphorous / chlorate mixtures only used in toy caps these days. It was safer to handle when wet than armstrongs mixture so saw some use in large globe torpedos before they were banned. Most sulfides sensitize chlorates (and perchlorates) pretty badly but realgar is on its own level from all the data I've been able to find. Whether this is structural or due to an extremely low ignition point, I don't know... good documentation is hard to find. It's probably dangerous in certain mixtures with potassium nitrate as well, but in pyrotechnics so is everything. Descriptions of it in yellow smoke star mixtures (with potassium nitrate) seem to indicate that it does as much to keep combustion going as the oxidizer.

I can't find much about orpiment sensitivity, it seems to have fallen out of use even longer ago but the two are usually interchanged in the few formulas that use them, depending on the country / author.

I've had a terrible time finding any information on the emission spectra of diatomic arsenic compounds in flame, but it was widely used in the form of paris green and copper arsenite for production of blue with potassium chlorate as an oxidizer. There's yet another confusion there, since Izzo's book (in Italian) differentiates between uses of the two and refers to copper acetoarsenite by another name, while American books call copper arsenite Paris green (which it isn't from a pigment standpoint). These type of formulae need a chlorine donor in addition to the potassium chlorate to perform optimally (and because they just weren't toxic enough for pyrotechnicians already and chlorate is incompatible with the others that were around at the time, and probably because of blue / near-UV emission from mercury salts, calomel was usually used). That's sort of veering off topic, but:

I found a patent from the 1970s that was unusually well documented on the usage of cast molten eutectic nitrate mixtures for a few colors of flares that's also relevant. The first patent by the authors noted unexpected emission spectra from eutectic nitrate mixtures (probably most notably the suppression of the sodium line in cast melts containing sodium nitrate and some other low-melting alkaline nitrate)... In their next patent, they used 40% of a eutectic mixture of either KNO₃-Ca(NO₃)₂ or KNO₃-LiNO₃, 20% powdered magnesium, and 40% realgar as the color producing agent which is mentioned as producing a deep blue. While potassium is capable of producing mauve under the right conditions and calcium has some strong blue lines as the pure element, normally neither can be used this way... and lithium is pretty much red. When they attempted to use paris green instead, it produced an inferior color (probably greenish, and copper compounds + magnesium metal are usually a bad idea anyway despite how anhydrous this will end up). While probably not usable in "normal" pyrotechnics except possibly parachute flares due to the need to cast it into a thin aluminum canister, all other mentions of realgar only use it to produce white light, yellow smoke stars, or odd glitter-like branching effects (Shimizu mentions its superiority in Senko Hanabi and writes off the toxicity due to the extremely small amount of composition despite it being a proximity firework, Izzo uses it in a lampblack star to produce a sizzling effect although it isn't described well, etc) so it's notable to see mention of it for color production.

While I could probably come up with enough material for a chemical article (I think I just did, aside from full citations) it would be mostly obsolete pyrotechnics usage which generally isn't too useful to people who don't already know about it. Even if it produces a great blue, so do any number of far safer to handle copper compounds well-known formulas. As a pigment it's only used for restoration, with the only supplier of pigment-grade material only selling to museums, and rarely since it'll eventually change to the beta form or react with neighboring paints and I'd expect that outside of rare cases it would be preferred to use a permanent inorganic pigment that's a color match instead. A Shortfall Of Gravitas (talk) 02:52, 15 December 2025 (UTC)

That is a lot of information. About H2S, our freshman labs were once plumbed for H2S to facilitate qual inorganic. I have a big cylinder - not a lecture bottle, a chubby cylinder in my own lab. We recycled our H2Se cylinder several years ago. The brief Brauer prep of As4S4 makes it seem easy. News to me. I dont think that it is soluble in anything, even CS2. It is strange for a compound to be sublimable (implying modest lattice energy) yet be insoluble in all solvents. The far less symmetric P4S4 is cited as an example of systematic synthesis of P-S rings. The P-S cages are more soluble, reflecting the diminished vdW bonding. Several preps of S4N4 are available, rumor is that purer samples are more sensitive than impure samples. Chivers and Finnish groups have investigated Se4N4. They also investigated Te-N rings are also developed but with R groups on N, imides. A big driver in that theme, at least a long time ago, was the high electrical conductivity of (SN)x and the prospect that we'd replace copper with cheaper material. I cannot contribute anything on pyrotechnics, which lures diverse people to dabble with chemicals. It's all about atomic emission, which is barely chemical in my book. --Smokefoot (talk) 13:09, 15 December 2025 (UTC)

The pronunciation of "realgar" in English

Probably the pronunciation of this word as represented in the recorded version at the top of this article is correct in whatever language that person speaks, but probably not in English. Play it for yourself, then imagine saying it this way in a high school chemistry class.

I don't know how to change it, but it needs to be changed. Ormewood (talk) 12:33, 22 March 2026 (UTC)

The audio file link to the pronunciation shows up on my phone's Wikipedia app, but not on my desktop computer. Ormewood (talk) 17:20, 23 March 2026 (UTC)