Sciencemadness Discussion Board

Cleaning Glassware

Duster - 15-12-2005 at 02:00

I was fairly surprised to find only a handful of posts on this subject when I did a search. I saw cairos acid, acetone, NaOH, and a few others all mentioned for cleaning glassware... Oh and Piric Acid. But overall, how does one best take care of their glassware?

My first thought was acetone (well, after water) for general cleaning of stubborn substances... Although I suppose a lot depends on what your cleaning out.

For example, one thing about distilling nitric acid, how do you clean the flask you mixed your acid and nitrate in?

Im sure this comes across as a newbie ish question but I think its important enough to warrent knowledgable anwsers. The last thing Im sure anyone wants to do is break an expensive piece of complex glassware because they tried to scrub out a substance when a solvet could have gotten it out (this happened a lot to my chemistry teacher in high school when students would pack in various things in small graduated cylinders and there was no way for him to get them out).

This shouldnt just apply to simple things like beakers and flasks, what about condensers, and various ground glass adapters? And tricks of the trade to get these clean?

Thanks for the help.

chromium - 15-12-2005 at 02:35

Buy some diswashing liquid from local supermarket. Also other types of cleaning liquids like those for cleaning enamel and glass can do wonders.

Use hot water and pieces of old newspaper in it. Shake well and if needed rub with woodstick.

Glass tubes, inluding some of bent tubes, can be cleaned by pulling piece of paper soaked into diswashing liquid and tied to long wire through tube.

I do not know what process you use for nitric acid but i have found that hot water when poured onto saltcake when its not completely solidified yet will solve the problem.

[Edited on 15-12-2005 by chromium]

Magpie - 15-12-2005 at 10:02

The traditional glassware cleaning solution (at least the one I learned in college) was a hot mixture of sulfuric acid and potassium dichromate. I used this successfully to clean out the helix tube of a condenser unreachable by any tool for mechanical cleaning.

I currently also have a 250 mL RBF from my nitric acid prepartion that has a waterline of grey plastic-like substance (OTC reactant impurity?). It is unaffected by acetone. It is not yielding to cold acid/chromate solution. But then again the solution is now green instead of the original orange so maybe the chromate is spent. Also I have not heated it. If this crud does not yield to hot, fresh acid/chromate I'm thinking that I will have to burn it out. :(

evil_lurker - 15-12-2005 at 11:57

I'm kinda fond of TCE brake cleaner myself for any kind of organic residues.

I know the shit works wonders on grease and oils of any kind on metals.

bio2 - 15-12-2005 at 12:14

There is a dishwasher machine additive "Glass Magic" for removing cloudy film that contains 21.6% phosphorous as phosphates. Label says contains sodium metasilicate, sodium tripolyphosphate and active organic chloride (unspecified).

This stuff works well almost as good as the old Alconox when it had high phosphates.
Takes off stubborn mineral deposits with a strong boiling solution that can be used over a few times. May take some hours for the worst residue.

BTW a flask damaged by boiling conentrated NaAcetate has not yielded to any treatment so far. It seems that the glass is perhaps badly etched or something.

Is there anyway to remove this residue appearing as scales on/in the glass?
I've tried everything I can think of for over a year with no luck!

BromicAcid - 15-12-2005 at 12:53

At my college we use isoclean to clean out basically everything. I've used a mixture of potassium dichromate and sulfuric acid but never needed it hot, a drop on a paper towel will char it so I figured it works good for removing organics of all kinds. I saw no mention of NaOH dissolved in EtOH so far, it's fairly strong. Personally elbow grease does it for me every time, I take stout metal wire and put a scouring pad on the end or glass wool or anything and pick at stuck on material. But of course it all depends on the stain.

Natures Natrium - 15-12-2005 at 14:31

I found a rather simple method of cleaning the inside of flasks and other pieces where it is very difficult to reach with any sort of tool is to take and dump a good quantity of table salt in (about 1/10 volume) and pour in enough acetone to leave a puddle above the salt. Then, shake like hell. Ive found this to be an easy way to remove even that brown manganate stain left over by permanganate oxidations, and the scrubbing action of the salt removes tars and other nasty junk that wont dissolve in any solvent. Its quick, easy, and clean up is a breeze; just dump the bulk of the NaCl/acetone out and rinse the glass out with water. Instead of acetone one can use water with an excess of salt (cheaper, more enviro-friendly), but I find that it is less effective than with acetone.

DrP - 16-12-2005 at 08:11

Never tried salt and acetone - think I might next time I get something stuck in some glassware.

We used to use a strong HCL acid bath (let soak for a few days) followed by a rinsing and then a base bath - NaOH/IPA/H2O This was quite effective but I never really liked having these baths sitting either side of the sink - people would just let stuff build up ib them. Our post doc said they removed the surface hydroxyls from the glass so as not to interfere with the reactions he was doing. (?)

fizzy - 16-12-2005 at 09:58

This site recommends KOH or NaOH in alcohol.

If you look around that site you will find some interesting low level experiments. I particularly like the one about detecting urea in stinky gym socks.

lacrima97 - 16-12-2005 at 19:16

I know that H2SO4+H2O2--->H2SO5?+H2O has dissolved cloth, and I have used it at work before for cleaning out the pans that the dumb cooks burnt up. That mix was the only thing that could ever get that charring off.

ADP - 18-12-2005 at 06:55

I know that H2SO4 + H2O2 --> H2SO5 + H2O at temperatures lower than 10 degress celcius but I'm not sure what happens at higher temps. I'm sure that between the oxidizing power of H2O2 and the dehydration power of H2SO4 it would remove the toughest gunk and grime.

chromium - 25-12-2005 at 04:24

Oxalic acid can be used to remove manganese oxides that are left from peramnganate oxidations. Just did this with great success. I used toiletry cleaning fluid that is essentially mix of detergents and oxalic acid. Left to stand for night and all MnO2 dissolved without any mechanical action.

[Edited on 25-12-2005 by chromium]

[Edited on 25-12-2005 by chromium]

NJF - 25-12-2005 at 06:46

I find that lots of hot water and gentle scrubbing will remove most things, IF the stain is easily accessable. If not, try boiling the glass in a pan of water for an hour, that gets most things off in my experience.
Acidic oxidisers should be good for organics, as others have mentioned, but save dichromates for more interesting purposes. Try persulphate PCB etchant with some sulphuric acid, or Fenton's, or something like that. I wouldn't like to regularly use hydroxides for cleaning glass, it might make all your stuff go gradually cloudy (I like my glass shiny :D). Although it would be very gradual, and wouldn't really matter unless you were using diazomethane or something (on a side note, have you seen glass for work with diazomethane? Flame-polished glass joints are sexy).
Some of the nastiest stains are from transition metals. Hydroxides and oxides can get ppted right onto your glass, and they can be a real bitch to get off. I have never tried, but something like really hot sodium thiosulphate solution might work.
Glass for high vacuum work is commonly cleaned by boiling it in nitric acid, and if you want REALLY CLEAN glass, put it in a belljar, pump it down to a few mBar, and apply RF power liberally. Nothing cleans glass like atomic oxygen at 30000*C :D.

The_Davster - 25-12-2005 at 11:21

I also use just lots of water and mild scrubbing for most things, but when I am working with metal oxides those do not come off well at all so I just use the acid waste from nitrations of various phenols. I then use HCl if the waste acid does not take off whatever stain. Under extreme circumstances I will very gently use steel wool to get off a stain, but I do not like exposing my glass to such things.

neutrino - 25-12-2005 at 11:54

>I do not like exposing my glass to such things.

What’s the problem with steel wool? Glass is generally harder than ordinary steels, so there shouldn’t be any scratching.

When cleaning <b>really</b> stubborn stains that nothing else will touch (like oil baked on at 300*C), I’ve often resorted to <i>very</i> hard scrubbing with steel wool. I have cleaned a certain Petri dish like this at least a dozen times and have yet to notice any damage. (Except to the joint in my fingers.) :o

lordmagnus - 15-1-2006 at 17:19

Simple green works well to remove allot of stubborn stains, for baked on goop, or mineral deposits I use (super IRON OUT) sulfamic acid powder, you can make a pretty strong mix to soak a really bad spot for several hours, smells like ass though, and you need some ventilation with it, then I run glassware through the dishwasher with some citric acid crystals, and some sheeting agent for hte final rinse usally.

neutrino - 15-1-2006 at 19:22

What exactly is this 'green'?

Magpie - 15-1-2006 at 20:19

IIRC Simple Green contains butyl cellosolve. Cellosolves have the form: HOCH2CH2OR. No wonder that cleaner works so well. :o

Hexavalent - 7-1-2012 at 14:50

I recently did a steam distillation of orange peels to recover limonene, but, unfortunately, due to the heat of the hotplate some of the solid matter burned and stuck like hell to the inside of my new 19/26 1ltr boiling flask.

I emptied everything out, cleaned it with water and then added sand, followed by some more water.

This worked wonders - the boiling water pushed the sand around which lifted the stains and residues in no time!

Lambda-Eyde - 7-1-2012 at 14:59

I prefer using marble chips (used for generating CO<sub>2</sub>;) and a little dab of soap. Works absolutely wonderful, plus it doesn't scratch and the pieces are so large there's no problem getting it all out compared to fine-grained sand.

Edit: 19/26 is IMO a small joint for a 1L flask!

[Edited on 7-1-2012 by Lambda-Eyde]

Hexavalent - 7-1-2012 at 15:05

I bought a job lot of used taper joint glassware on eBay, everything was 19/26, including the mentioned flask, my 60mm liebig and all of the claisen adapters, still heads etc.

It is a nice size to have IMO - Goldilocks - not to big, OK for microscale stuff, not to small, nice for bulk solvent production.

Sedit - 7-1-2012 at 16:18

Use dirt, sounds funny but sand a little detergent and water into a semi thick slurry will slowly take off even the most stuborn caked on things with alot of shaking.

peach - 8-1-2012 at 03:41

What you use to clean it depends largely on what it is that's stuck in it.

There's no point using piranha and aqua regia if a squirt of acetone will do. Conversely, some of it is not going to come out with anything bar an option like that. E.g. one of the glass manufacturers recommends baking the glass at 480C in oxygen to remove free carbon.

It also depends what that thing is stuck to.

If it's a conical flask, getting in there with a scrubby brush on a stick is easy and fairy liquid (washing up soap) or biological washing liquid will work beautifully. Some bits of complicated micro glass, a scrubby stick is not going to physically fit in there.

Sintered glass is the biggest pain in the ass to clean, as the sinter is effectively a sponge to soak up crud, but an unsqueezable sponge.

Think about what is stuck to the glass, and then what might be the best way to remove it. E.g. metals, you can dissolve to a water soluble form with your acid of choice, greasy organic muck (like charred oil), that is a specialty of biological washing liquid. The same big name glass company also recommends using domestic dishwasher powders and liquids as an alternative to the propriety laboratory cleaners.

There are varying options based on how clean you need it to be. If I were filtering something for chromatography, I'd want the glass sparkly. Other times, it doesn't matter if it's grubby since what's going on is grubby to begin with and is inevitably going to need tidying up afterwards.

[Edited on 8-1-2012 by peach]

Neil - 8-1-2012 at 08:03

I've had interesting luck with hot 30% H2O2 + fresh iron hydroxide for removing waxy organic residues from flasks and sintered glass. It is slow though.

Hexavalent - 8-1-2012 at 08:40

Failing all of above, you decide to use a piranha solution. What composition is best?

peach - 9-1-2012 at 02:19

I don't bother to measure it out precisely, I use disposable 3ml pipettes - which I then rinse out and reuse. They're available in hundred+ bags for a few pounds and are exceptionally handy.

To clean sinters, I stand the item up in a jam jar (or something similar), add a squirt or two of 98% sulphuric, then a squirt of 35% peroxide, give them a swirl and let it stand.

I use two different pipettes for each of the components, and I keep the peroxide in the freezer. That not only helps prolong it's lifespan, but also means that it takes a little longer for the process to get started.

It does start, quite quickly. The mixture rapidly warms up and begins to effervesce. Things that look clean almost immediately begin turning brown, and possibly even black, if there is any trace of colourless organic material there. The mixture begins to sound like a freshly opened bottle of coke as it fizzes away.

With coarse sinters, the mixture will usually flow through them under gravity alone, within a minute or three. I simply remove the glassware from the jar and pour the mixture back through two or three times. For medium to fine sinters, particularly those that are clogged up, applying some very gentle suction to draw it into the sinter will help. I then leave it to get on with it's own thing rather than bothering to constantly cycle it.

You something may end up with something exploding using this method. I do not use hard suction and cycle it, because the shock of the hot mixture running through and then the sinter drying out is that kind of thing that could help something detonate (this is the same scenario that ended with a student being sprayed with bits of glass when a filter under vacuum exploded). I usually leave the glass to sit for hours or overnight, allowing the mixture to chew away at the dirt and decompose, and then rinse over and over with water to remove it. I tend to do the first rinse by gravity if possible, in an attempt to gently rinse anything potentially explosive out of the sinter and into a solution.

There is no point mixing up a hundred mls of it, as it only requires about 3-9ml to clean a sinter well. It decomposes so rapidly the entire lot will be dilute sulphuric by the next day, so there's no point storing it either. Even if you plan to use it immediately and end up needing more, it's better to mix it as it's used so it's always fresh when put into use.

I have tried the persulphate in place of peroxide method (NoChromix), but prefer the peroxide by a long way.

Hexavalent - 9-1-2012 at 10:28

Thanks for your input. And a word of warning for beginners - if you are new to chemistry, it is probably not a good idea to start your adventure into the world of science with such materials. They are hideously corrosive, toxic, produce toxic and irritating fumes and require full PPE including heavy nitrile or neoprene gloves, a chemically impervious apron or hellova good lab coat, chemical splash goggles and a face shield.

Glassware cleaning?

Dariusrussell - 26-7-2013 at 13:29

I recently got a hold of a used corning organic glassware set and two of the pieces are a bit dirty. One is a 125 mL RBF and the other is the vacuum takeoff.
I've read This Topic
and found a plethora of things to try. I already tried warm water and soap, Ethanol/Methanol, and acetone. Im guessing they havent been used in 20+ years so the stains are caked on pretty well.
Does anyone have a good easy next thing to try (ie Fentons, Piranha?)

The substance is white and powdery so not much help in identifying it.

In the pictures there is some water and condensation, if needed I can take more pictures once dry.
<img src="" width="600" />

<img src="" width="600" />

<!-- bfesser_edit_tag -->[<a href="u2u.php?action=send&username=bfesser">bfesser</a>: reduced image size(s)]

[Edited on 7/26/13 by bfesser]

crazyboy - 26-7-2013 at 13:46

In my experience a cup of sand with some water or cleaning fluid works well. Swish that around in the round bottom for a while and that works pretty well. Failing that some concentrated sulfuric acid with a bit of water usually works as well.

Rich_Insane - 26-7-2013 at 14:43

Try a concentrated NaOH bath. Use boiling water for best results. Be careful, over time, this treatment can weaken some types of glass... But I find that a warm base bath works well. If that fails, try sulfuric acid. Of course, you should try a couple different solvents before resorting to more corrosive agents. Acetone is good for cleaning (it evaporates off pretty quickly). Dichloromethane might be good too. I've used those two solvents in the past to remove organic residue in glassware.

bfesser - 26-7-2013 at 15:03

Quote: Originally posted by Dariusrussell  
I've read This Topic and found a plethora of things to try.
So you searched for and found an existing thread, but in defiance of all logic and perhaps even common sense, started a new one instead? I appreciate that you've done your research, but in the future, please reply to existing threads on your intended topic rather than starting new ones (if applicable). Thank you.