Peter, please ask Laszlo Siklos tomorrow morning, he may know the answer. M.

Hi Peter. I've used 4% OsO4 aqueous solution from Electron Microscopy Sciences (https://www.emsdiasum.com/microscopy/products/chemicals/osmium.aspx) and from TAAB Laboratory and Microscopy (http://www.taab.co.uk/pdf-products.php?cat_id=2&sub_cat_id=24&pdf_id=211), and both worked well for standard specimen preparation for transmission electron microscopy.

Hope it helps.

Thank you, Robert.

Hi Peter, I always preferred to have a stock OsO4 chemical in crystalline form in glass ampules for longer storage, regardless the manufacturer or supplier. It requires special handling procedure during making a solution. Already dissolved OsO4 may degrade after some time in vials (possibly not in sealed ampules) and requires careful handling and reasonably quick consumption. Any, even slight discolorization of the unused OsO4 solution should be taken as a sign of its degradation.    D.

@Peter: Differences in prices MAY BE / are  a consequence of daily / weekly changes of "precious metal" prices at stock exchange /commodities market(s) and [calculation via) US-Dollar-rate. Differences in selling prices of different companies (consider the ONLY few natural sources OsO4 comes / is provided really.....) are as huge as 5-10 times. Naturally the price varies for different (crystal) weights due to commercial and saftey packaging (0.1g is much more expensive than 1.0 g packages)   In the 1990ies, when I had to purchase OsO4 I wrote to 5 suppliers for OsO4 (crystals), requesting a quote for identical amounts of the product for a fixed amount of money (the latter was Austrian Schilling 15,000.-  and I wanted 50% 1 g ampoules, 25% 0.5g ampoules and 25% 0.1 g ampoules:  their offers (it turned out that 2 of those sellers had their OsO4 from other offering companies!) varied from 24g only to 75g in total! Needless to say which offer I accepted....  Ampoules can be stored in the fridge over a long period of time.... and handling / making solutions by your own MIGHT be hazardous ....but only to the unexperienced and timid scientific worker (:-))   If you want to read more about that history.....just request via RG-Message system... Thank you and my best regards, WM

I use only crystals of OsO4. Crystals can be stored for many years. I have experience only with Electron Microscopy Sciences, mostly because I had ordered OsO4 just a few times due to its good shelf life (did not have a need in experimentation with different sellers).

EDIT: Just checked price, 1g for $35. It means 25 ml of 4% OsO4 for $35. Definitely much cheaper than solutions. And freshly made every time.

Honestly: Needless to say that I second Vladimirs opinion regarding storing and making of solutions.   .... and I have had also ONLY OsO4 crystals in storage over YEARS.... ( 4 °- 6 °C ). For our  lab-and diagnostic spec-prep. purposes I bought only two times OsO4 crystals in appropriate amounts when the US-$ was 'low': in 1990 and around 2002 or 2003 (but do not remember 100%). The last amounts of 1g an 0.5 g I used up in my last year of profession (2015).

A price of US-$ 35.- / 1 g being a reasonable and most everywhere an affordable price...(:-))  

NB to what I said/posted above in my reply #05:  

approx. 13,6 Austrian 'Schilling' were the changing rate for 1 € .....

Thanks for the valuable answers.

Dear Peter, you're welcome. Since you are located in Hungary you might think about getting into contact with the German representative of EMS, locaterd in MUNICH, Bavaria....(not knowing a representative either for Austria or Hungary) cf. http://scienceservices.de/en/; for OsO4: 

http://scienceservices.de/en/sds (or  MSDS: @ http://www.emsdiasum.com/microscopy/technical/msds/19100.pdf

In addition I would like to add that usually the purity of OsO4 is (at least should be) 98%-99,9% Os... lower purity not recommended.

Further sources to be studied might be interesting:   https://www.ceimig.com/osmium.html 

http://www.polysciences.com/default/catalog-products/life-sciences/histology-microscopy/fixatives/osmium-tetroxide; (= http://www.polysciences.com/default/catalog-products/life-sciences/histology-microscopy/fixatives/osmium-tetroxide/osmium-tetroxide-4-solution-5-x-10ml/ )  or there also (to see also the price differences due to costly packaging) : 

Osmium tetroxide, crystalline, 99.95% - 10x1/2g

Osmium tetroxide, crystalline, 99.95% - 10x1/4g

Osmium tetroxide, crystalline, 99.95% - 10x1g

Osmium tetroxide, crystalline, 99.95% - 5x1g

https://iaspub.epa.gov/sor_internet/registry/substreg/searchandretrieve/advancedsearch/externalSearch.do?p_type=CASNO&p_value=20816-12-0

https://pubchem.ncbi.nlm.nih.gov/compound/osmium_tetroxide and there:   https://pubchem.ncbi.nlm.nih.gov/compound/osmium_tetroxide#section=Chemical-Vendors

https://www.fishersci.ch/ch/en/products/I9C8K3F6/osmium.html  and /or : https://www.fishersci.com/shop/products/osmium-tetroxide-99-9-trace-metal-basis-acros-organics-5/p-4229010 (to find out 1 g of OsO4 @ ACROS is listed actually as 1 g Each for $262.36  ![compare to Vladimir's reply!) 

Disclaimer: no affiliation to any company mentioned here, and therefore - naturally - also no financial interest!

It pays off to compare as many as possible suppliers (and their online-catalogues) of OsO4 and to ask them for their / a quote  to arrive at a really cheap cost of OsO4 (and - with regard to special packaging and delivery by mail it might be better to purchase at least  10x1 g rather than 5 x 1g....   Storage of self-made OsO4-solutions I can recommend to be done in 'double capped (brown glass) acid etch tube' [which additionally should be wrapped appropriately with parafilm]. And my last recommendation is:  only store hydrous solution of OsO4 (one can freeze easily and thaw in time right before mixing the working solution (which usually is a BUFFERED solution). Further recommendations available on request.

Best of luck and success, WM

Dear Peter,

I would add another company, well-known at the EM field (Ted Pella):

https://www.tedpella.com/chemical_html/chem3.htm

We routinely order from this company and everything is OK.

All the best,

Łukasz