Introduction: Really Beautiful Swimming Ferrofluids
This is a description of how to make ferrofluids that swim beautifully in vessels full of clear liquid. There are many on-line descriptions of how to make up ferrofluids, which are liquid magnetic materials that form into beautiful shapes when exposed to a magnet. However, the common approaches using bulk iron oxide, laser printer toner, or dissolved magnetic tape really give you something more like ferrosludge; they are rough clumpy materials that are far less fun than the elegant effects you see in swimming-type ferrofluid devices. Here you will learn the essential secrets to getting the real thing; a ferrofluid blob suspended in a clear liquid that swims freely, forms beautiful shapes with a magnet, and does not stick to the vessel. The secrets are in how to prepare the ferrofluid, how to make the clear suspension liquid, and how to prepare a glass vessel. You need to do all these steps correctly or the ferrofluid will stick to the walls of the vessel and make a mess. The photo above shows a ferrofluid display I installed at the Chabot Space and Science museum in Oakland, CA in 2013, which is still working perfectly.
Step 1: Materials
1: Ferrofluid: Ferrotec, Inc, (www.Ferrotec.com) makes the ferrofluid. You can also obtain the fluid from Amazon and other retailers. The Ferrotec process is sophisticated nanoparticle chemistry that gives radically better results than you can get in the kitchen with crude materials. Ferrotec EFH1 material is 5% Fe2O3 nanoparticle precipitate from the reaction of FeCl3, ferric chloride, and NH3, ammonia. It is stabilized with the addition of 10% surfactant, a fatty acid like oleic acid; the exact formula and process is proprietary. Stabilization means that the nanoparticles are coated with surfactant, which prevents them from clumping together. The balance (85%) is a hydrocarbon oil, like kerosene, which serves as a vehicle to liquefy the ferrofluid.
2: Saturated brine solution for the ferrofluid to swim in. Commercial providers have proprietary formulas for this solution, but saturated brine (pure sodium chloride in pure water) works extremely well and is stable for years. Use Kosher salt or pure NaCl to make this; ordinary table salt contains anti-caking agents that make the solution cloudy. You can use alcohol based suspension solutions, but the much lower surface tension of these suspensions causes the ferrofluid to form stringy, spiky shapes with a magnet, and not the graceful smooth shapes that most people desire.
3: Clean glass vessel to put the ferrofluid + suspension liquid in. The bottle, jar or whatever you use must be clean, and it helps to prepare it chemically. The vessel should be sealable with an airtight cap.
4: Clean glass container to prepare the suspension solution, Petri dish or equivalent, stirrer, lab gloves, hot plate or electric stovetop, glass thermometer, pipette (plastic is fine), scale.
Step 2: Prepare the Ferrofluid: Secret #1
EHF1 from Ferrotec is true ferrofluid and the best material, but even it can be improved for this purpose. EHF1 Ferrofluid from other sources may be cut with additional kerosene, which definitely requires reduction. Careful heating will evaporate some of the lighter hydrocarbons in the kerosene, and make the ferrofluid less sticky on glass and more viscous, which improves the visual effects.
As a starting point, for a few hundred cc sized vessel, you probably want at least 10cc of ferrofluid. Take the amount of ferrofluid you plan to use, put it in a shallow clean glass or metal dish (pipette transfer is good), like a Petri dish, place it on a hotplate at 100C until you reduce the weight of pure EHF1 by about 10%, or more for diluted ferrofluid. The result will be noticeably more viscous. Do this in a ventilated area to avoid kerosene fumes and fire danger, and use an electric hotplate or stovetop.
Ferrofluid is seriously messy; no matter how careful you are, you are likely to get black stains on hands or gloves, clothes, countertops, etc. It just is.
Step 3: Prepare the Suspension Solution: Secret #2
Clean a glass container with a harsh cleaning solution, like hot water and ammonia, until water does not form beads on the glass, but runs off in sheets. Rinse in hot water and dry. Pour an amount of room temperature distilled water into the container sufficient fill the vessel you plan for your ferrofluid device. Pour in Kosher salt steadily and stir with a clean stirring instrument (spoon just out of the dishwaher, clean glass rod) until no more dissolves, no matter how long you stir. Some undissolved salt will remain in the water. Water at 20C will dissolve 35.7 grams of NaCl per 100 ml of water. This is almost 6 oz/pint, an amazingly large amount. You may scoop out the undissolved salt and add a small percentage of distilled water to the saturated solution, so that salt does not precipitate out of (the resulting slightly less than saturated) solution.
Step 4: Prepare the Vessel: Secret #3
Plastic vessels don’t work; the kerosene will stick to them. Clean glass vessels are the best. We have had good success with vessels directly from glassblowers, and thus directly out of annealing ovens. We have also found that vinegar jars work very well, probably because they have held a weak acid for a long period. If you use another type of vessel, clean it as in step 3 first. It may help to put it in an oven or kiln, cycle it to high temperature (300C) slowly enough to avoid cracking, and then put vinegar in it for a day or two, and rinse with distilled water afterwards. Finally, put the brine solution in the glass vessel for a day or two before introducing the ferrofluid; all of this limits the tendency of the ferrofluid to stick to the glass.
Step 5: Final Assembly
Pour the brine into the vessel and fill to the top. Do not allow undissolved salt into the vessel. With a pipette or small diameter clean tube, transfer the ferrofluid into the brine solution by putting the tip of the pipette and inch or so under the surface of the brine and releasing droplets of ferrofluid, which will sink to the bottom. The vessel will overflow, which is good. You may get some ferrofluid floating to the top of the water; suck it away by touching the water with a paper towel. Seal the vessel with a small air bubble at the top to give the brine a little room to expand with temperature. Avoid tilting the vessel so the ferrofluid can contact the cap, as it will tend to stick there.
Step 6: Voila!
Voila! This jar is 4 years old, with no sticking, and with beautiful magnetic effects.
Tip 20 days ago
I am happy to help. There is no special problem with air above your solution, but what you must avoid is having the ferrofluid attracted up to the air-glass interface. As long as the ferrofluid stays in the solution and does not touch the air-glass region, you should be OK. You actually cannot usually have a vessel sealed with no air, because air acts as an expansion volume if the water changes temperature. You will want ot make sure your electromagnet is well down into the glass that protrudes from the lid, so that the ferrofluid
is not drawn up to the air. The ferrofluid will coat glass that is in the air.
Where are you? I'd love to see a photo of your finished project.
Question 20 days ago
Hello, I hope you are still answering questions about this.
I have an ambitious project in mind in which I want to put suspended ferrofluid into a spheric glass container and then have a glass lid with a void elongated shape that reaches inside the sphere. In there I would put electromagnets so that the ferrofluid would form shapes in the middle of the sphere (around the glass containing the electromagnets). My main question is about having a sealing lid. For how my glass object looks I will have an open object and air will touch the solution. How much is that a problem and why? Thank you so much in advance for your reply and even more so for making this instructable available :) Giada
6 months ago
If you want a ferrofluid that works much better then Ferrotec look on Amazon for ferrofluid from a company called Consolidated chemical and solvents. There stuff is oil based and does not need to be concentrated. It useally works with a clear liquid such as water and a little bit of alcohol
Reply 6 months ago
From the looks of your ferrofluid, you are getting a very spiky pattern, which is typical of the alcohol/water environment. My approach with brine gives a more blobby pattern, indicative of greater surface tension at the water/ferrofluid interface. This may be a matter of taste; if you like the spiky apparance, then alcohol is the way to go, but if you prefer blobby, then use brine.
Tip 9 months ago
You seem to be pretty aware of materials and chemistry, which is good. You want to clean the glass so that water forms a clean sheet on it, with no isolated drops. Drops indicate contamination. if you clean the glass in an ordinary dishwashing machine with hot water, that should do the job. If you then have acces to a kiln that can get up to 750C or so, you might want to try cooking the glass in that, but it should be unnecessary.
Even the good EFH1 from Ferrotec is too thin, and needs to be reduced to make it more like honey. It will take a few hours at 100C; be sure to work outdoors. If you do it in your mom's kitchen, she willl probably call the police and tell them to throw you in jail.
I'm not sure why vinegar bottles work; I used them because they were cheap. Maybe there is some magic involving acid, or maybe not. In principle a basic solution should etch the glass more than an acidid one, unless the acid is hydroflouric, which you should not experiment with.
Tip 9 months ago
Here are some suggestions. Resellers sometimes add kerosene to dilute the EHF1; I don't know if yours did, but in any case, I don't think that 30 mins at 100C will do much to increase the concentration. The ferrofluid needs to b reduced quite a lot. I did not do scientific analysis on it, but it should be more like honey when reduced enough.
To test the EFH1, you might buy a bottle of white vinegar, rinse the bottle a couple of times in hot distilled water, put in the saturated brine, wait a couple of days, then add the ferrofluid. If it still sticks badly, it could be a problem with the ferrofluid. If it is OK, then your problem may be with the glass vessel.
When you clean the glass in an ordinary oven, it does not get really very hot, so it just burns contaminants onto the surface, but does not remove them. Therefore, you should clean in hot alkaline solutions and rinse with distilled water before heating in the oven.
The reason I used Kosher salt is that in the US, ordinary table salt has some kind of organic stuff mixed with it to prevent clumbing due to water absorption. Kosher salt does not, at least not here. All you need is some kind of pure salt. NaCl from a chemical company should also work.
Glass has a thin porous layer on its surface that can be passive or active with respect to EFH1. The object here is render this outer layer clean and passive. I have had success with common soda-lime glass and with borodilicate laboratory glass. If you are using another glass, like hand blown studio glass, you may get different results. I have had ferrofluid in a vinegar bottle with no staining at all ever since I wrote the original Instructables article.
Please let me know if you have further questions,
Reply 9 months ago
Thank You for the suggestions!
I already have bottle after white vinegar sitting with a brine to test in 2-3 days. The only downside is i cleaned it with tap water. I will to the same with destilled to compare.
Is the isopropyl IPA99,9% good as an alkaline to clean the glass with? I can boil the vessels inside IPA for some time, dry out and heat in oven. What about preparing the glass container for suspension, i bought ammonia but solid solution, should i mix it in hot water and clean it as well?
As for the suspensions:
Pure NaCl seems to be more friendly to a ferrofluid, it is very clear, fluid is fast, there is posibility to create micro spikes. The salt solution makes it live longer for some reason but the ferrofluid is more like a ball inside. It still creates spikes and flows around but it surely acts a little bit worse (vessels were from the same batch of cleaning). I will do more trials with these suspensions.
I also bought borodilicate glass bottles to see if there will be any difference.
According to the fluid - the reseller got very upset when i asked about originality of the product. Claims that ferrofluid comes directly from Ferrotec as the company is affiliated for several years and it is the best one in the marke (https://magnametals.co.uk/).
9 months ago
Hello, Thank You very much for the tutorial You provided!
I have still some issues with ferro staining to the wall of glass vessels.
I bought EHF1 ferrotec ferrofluid from magnametals reseller (recommended by ferrotec). Here are the steps that i made to create the solution:
1. Creating the suspension:
I took a glass vessel and cleaned it in hot water. Then i introduced destilled water, and added pure NaCl until it stopped desolving no matter how much i stir. The solution sat there for about 4 days.
2. Preparing the glass vessels:
I put the glass vessels into the oven for heating at max temp for about 4 hours, cool it down to the room temp. After that process i immediately put sodium percarbonate about 3/4 of the vessel and filled the rest with destilled water. It sat about 24hours. I cleaned the vessels from sodium percarbonate in the tap watter and immediately added the suspension solution to avoid any oxidation.
I have reduced the EHF1 ferrofluid on the heating stove for about 30 min in 100C. It became a little bit more viscous. Cooled it down to room temp.
4. Making the full solution:
After the glass vessels sat down with suspension solution for 24h i added the ferrofluid. It was fully functional for about 20 minutes or so. After that it became stainy in some places. Wherever fluid stays for a longer period of time it creates a brownish stain.
I have introduced the ferrofluid to the other vessel which sat down with solution for 48h. Results were the same.
I have introduced the ferrofluid to the vessel with other solution (brime with destilled water and NOT iodized salt) In my country, Poland, there is no place to buy molten kosher salt. So the ferrofluid started to stain a little bit on the bottom after 15h. It was fully functional before that time, but i could see that it is more flexible, fast and movable in NaCl solution. In salt solution it acts like a spongy dot.
Now the questions @rogercarr:
1. What can i improve in creating suspension? in the comments you mention harsh cleaning with hot watter and ammonia. I bought bicarbonate of ammonia NH4HCO3 99% clean. Should i mix it with the hot water in the vessel and then heat inside the oven before i introduce destilled water and NaCl?
2.What can i improve in preparing vessels for the fluid? Should i try the vinegar solution after baking in oven? or Bake in oven, clean with OxyClean or pure sodium percarbonate as i did before and then add vinegar?
3. What can i improve in making the ferro, should i try to reduce it even further? For how long do you suggest to keep it over 100C? Judging by the looks reduction for about 20% is hard to judge, especially when the karosene is sticking to the glass walls during mixing to prevent sticking to the bottom.
Maybe You have a seller that You recommend to buy the ferro from?
I would apperciate every suggestion from You guys. I have been going crazy for a long time for the ferro, came up with cool results but they are not fulfilling my satisfaction.
Have a great day.
Question 1 year ago on Step 2
Instead of heating it up on the hot plate, could I just light it on fire and burn off the excess kerosene?
Answer 1 year ago
An interesting idea, because it would selectively consume the lighter fractions. Downside: hard to control and unsafe. Try it and let me know how it works. Do it outdoors.
Question 1 year ago
"Voila! This jar is 4 years old, with no sticking, and with beautiful magnetic effects." Are you saying that this jar with the ferrofluid is 4 years old or just the glass jar is 4 years old?
Answer 1 year ago
I assembled the jar with contents more than four years ago. I had purchased the jar shortly before I filled it. I’ve done nothing to it since the original fill.
Question 3 years ago on Step 5
Hello and thank you for this tutorial.
I'm trying to make a ferrofluid display.
So I made the satured brine solution with distilled water and pure NaCl.
I bought Ferrotec EFH1 ferrofluid, but I didn't reduce it because I live in apartment.
The ferrofluid doesn't sink to bottom but floats.
Is it normal ?
Is it because I didn't reduce the ferrofluid ?
Answer 3 years ago
If your ferrofluid floats, that indicates it has too much hydrocarbon (kerosene) vehicle relative to the iron oxide. You must reduce it. You will have to find a well ventilated place to do this; do you have a balcony? The kerosene fraction that volatilizes is not all that
toxic, but nothing you want in indoor air space where people can breathe it. Some third party suppliers of EFH1 cut it with additional kerosene, which is sleazy, and may be the source of your problem.
Reply 3 years ago
Thanks for aswering so quickly.
Yes I have a balcony.
It doesn't smell too much ? I don't want to have neighbor's complaints.
How long does it take to reduce the ferrofluid ?
Reply 3 years ago
You should not do anything to annoy your neighbors or cause a fire hazard. The time
you need to reduce the kerosene depends on how hot you make it. I have only done it quite slowly at lowish temperatures (150C or so) for several hours. You do not want it to boil. It will smell less at lower temperatures, but will still be noticable.
Reply 3 years ago
Thank you !
Question 4 years ago on Step 7
Thanks for the protocol of your project. I'm working on a display for an exhibition too. now. For this I use petridishes and followed youre procedure. The FerroFluid stains heavily the glass surface. Now I've tried different protocols and variables: different supplier FF, sugar, ethabnol, bottles. All without succes. What make the glass so sticky and how do I prevent this?
Answer 3 years ago
Try polishing with cerium oxide.
And even better with Tio2 coating.
Reply 4 years ago
A couple of comments. First, try putting your petri dishes in an kitchen oven at the highest temperature it can do for an hour or so; this should give you fairly clean glass. Then allow the glass to soak in the brine solution for a day or two before adding the ferrorluid. Your glass must be so clean that water runs off it in sheets, and does not form drops on the surface. The vessels I made years ago are still going fine, with no staining whatever, both in vinegar bottles and Pyrex.
Where did you get your ferrofluid? It may be of poor quality or may be dliuted excessively with hydrocarbons. Did you cook it before use to make it thicker?
Buy an ordinary bottle of white vinegar and wash it out thoroughly. Put the brine in it overnight, and then the ferrofluid. This technique should work very well. If that stains the glass, then I suspect the ferrofluid.
Please let me know how it works out.