Homemade Plastic




About: Just a dude who likes making things :)

This is a quick and simple method for making your own general-purpose plastic. The constituent ingredients are milk and vinegar. That's it. The total cost is less than $10, possibly less than $5 if you can get a good deal.

The plastic is moldable, and has a consistency of soggy cheese (I certainly hope I never encounter cheese that's anything like this!). When all is said and done, it should take you about 10-15 minutes to make the plastic (less if you make a small amount), 10 minutes of cleanup, plus 2+ days to allow the plastic to dry. As always, your milage may vary.

As for the final product's strength and whatnot, I would classify it as "okay." If you roll it thin (as I did in this instructable), it can easily be snapped in half, though it will probably survive a small drop on to carpet. Thicker pieces seem to be more resilient against average abuses - no problem dropping on to carpet, and if it's thick enough, you wouldn't be able to snap it in half. A blow from a hammer or other such object would quickly shatter it, though.

All in all, I would say this is mostly useful for folks looking for a fast and dirt cheap alternative to much better products available to the average joe. It's definitely not for something that will be handled on a daily basis - good enough for light decor, not much else.

This is my first Instructable, so bear with. Constructive criticism is always welcome!

Step 1: Ingredients & Utensils

This doesn't require anything fancy.

Essential Items:
Large Pot
Larger Pot (needs to be the same size as the other, or larger).
Spoon, preferably plastic or metal
Strainer or Colander, the finer the better
Stove or other item with which to simmer milk.
Paper Towels, lots and lots of paper towels

Handy, but not necessarily essential, items:
Wax Paper (good for rolling and shaping on. Water and other liquids bead up on it for easy clean-up; also non-stick with the casein)
Aluminum Foil (good for certain types of molds)
Rolling pin (if you're going to make a flat sheet of plastic)

Before you begin making the plastic, it's important to know what you're intending to make. By knowing what you're final goal is, you can make the preparations for the mold before you have a sloppy wad of plastic on your counter.

For this Instructable, I am making a curved piece that will fit on the front bezel of my computer case. Since this is beyond the scope of this particular instructable, I'm going to gloss over what I'm using. My mold is going to be the front bezel of the computer case, covered with aluminum foil. The plastic will dry nicely on top of it, and the aluminum won't shrivel or wrinkle when it gets wet as the plastic cures.

How much milk and vinegar will you need? The basic ratio that I follow is 1 TBSP of vinegar for every cup of milk. (16:1 ratio, milk to vinegar)

1 cup of milk will produce a puck of plastic about 2" in diameter, 1/8" thick.

To cover my case bezel, which is about 6 inches wide and 8 inches tall, I am going to use 8 cups of milk (and therefore 8 Tbsp of vinegar).

Step 2: Heat It Up

If you've never heated milk before, it's important to know that if you heat it too fast, it will start to burn on the bottom of the pot. To bring it to a simmer, it's best to keep the heat down to about 50-60%.

I don't follow my own advice, and use full heat, because I don't want to wait.

While the milk is heating, be sure to stir it occasionally, so it doesn't burn. Also, if you're heating more than one or two cups of milk, measure the vinegar out into the cup while the milk is warming. This is personal preference, as it makes it easier to pour the vinegar in all at once, rather than measuring it out in a hurry.

During this time, you may need to pander to a needy cat, if one happens to be around.

When the milk nears boiling, you will notice a foam forming on top of the milk, as well as a little noise coming from the pot. Steam will start to appear too.

Once you reach this point, turn off the heat, pour in the vinegar, and stir. You will immediately notice chunks of casein forming. Stir it for another thirty seconds or so, for good measure.

Step 3: Strain

Slowly pour the heated liquid through the colander and into the larger pot. Most of the chunks of casein will get caught. We pour slowly to avoid splashing the plastic-loaded liquid into the sink. Something tells me that chunks of this stuff in the drain is not a Good Thing(tm).

Once you've poured it out (don't worry about what's left in the bottom, we'll get to that), gently shake the strainer, and swirl it around a little. Most of the casein will lump up in the bottom, pulling itself out of the holes. Make sure a majority of the liquid is strained out, but don't press it out -- the casein will just get stuck in the holes, and make it harder to get out.

Now that it's all clumped together, dump it out on some wax paper.

If you have a super-porous strainer like mine, you may want to pour the liquid through the strainer several times. Doing it a second time pulled a chunk about 1/4 as large as the original mass; that's a nice addition.

Step 4: Sop Up the Excess

After you've strained all of the casein out of the liquid, you'll want to soak up some of the remaining juice in the mass on the wax paper.

Use a few paper towels, and press gently on the casein. The liquid will spill out like squeezing a sponge. Be careful not to make it too dry, because it will become difficult to mold if it's too dry.

Step 5: Mold!

At this point, you're ready to do whatever you want with the plastic.

It will take about two days to cure, but if you're using a mold where it cannot easily breathe, it will take longer.

One thing to watch out for is that the casein will warp when it's drying, especially if you have it rolled out into a sheet. It's best to put a weight on it. Watch out, though, because it will seep a milky-vinegary scented liquid into whatever is holding it in place. I used a heavy programming book...and it now has a funny smell to it. Awesome.

For my project, I just need to roll the casein out and let it dry.

Lay another sheet of wax paper over the casein. Use a rolling pin to spread it out. If you didn't dry it too much in the previous step, it should roll nicely, without many cracks or chunks.

Finally, I pressed it between two sheets of aluminum foil, and curved it across the bevel I'm using.

Give it a few days to dry, and it'll be ready to go. This is critical. Depending on how you wrap/mold your casein, you may find it takes more than a week to dry. Wrapping mine in foil took two weeks to get remotely dry. As is expected, the thicker it is, the longer it will take to dry.

I should also note that if you're making a flat piece like I am, the plastic will curl if you remove it from its mold before its dry. I made this mistake with this project, and ended up with a piece that was unusable because it curled.

The final product is quite rigid when it's thick (1/8 inch or thicker), moderately pliable when it's a little thinner, and brittle if it's paper thin. It's also sandable and paintable.

Go forth and have homemade plasticy fun!



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    282 Discussions


    10 months ago

    Have made this Milkstone many times and the instructions are mostly good and correct. However, if you use vinegar be sure to use white vinegar (less smell) and be sure to very gently rinse through your colander at least 6-7 times. Yes you may lose a little of the casein but trust me when it hardens you don't want the smell on anything you've made. Alternatively, you can substitute lemon or lime juice for the vinegar which saves the problem. I believe the rinsing process is what stops the end piece from going mouldy. I just heat up my milk in a microwave jug until just frothy as no burnt pans.

    I began by using an insert from a box of chocolates and pressed my small piece of casein into four or five of the small sweet shaped cavities. This produced some interesting finished shapes although I had to keep pressing them in regularly as shrinkage does occur. Got some nice little finished articles.

    At first the product created is very much like paneer or cottage cheese but rapidly becomes gel like and then harder and harder until like grainy stone. I recently made a batch adding a little food colouring and when it started to firm up inserted a cocktail stick which it held nicely to provide a hole. When completely hard I then removed the stick by twisting and then sanded the surfaces to make a small smooth necklace for my daughter. Great fun and yes, any mould you work will do. Only batch ever went wrong for me was when didn't rinse the vinegar off enough. I don't bother with formalehyde as its only my hobby and rather not use any chemicals. Have made handles for tools that have lost them and even my own tools.

    Great fun just be careful with any food colouring as can be messy!


    7 years ago on Step 5

    Are you sure this is truly casein?? My understanding is that casein is precipitated from milk by rennet, not heat. Heating whey with vinegar or other acidifier creates ricotta, which is not a cheese, as it contains no casein, but is rather the precipitated albumin and other (not casein) proteins. Galalith is made from casein and must be fixed in a formaldehyde bath; it is not moldable.

    1 reply

    Reply 3 years ago

    any acid in warm or hot milk will precipitate the casein protein the largest mass of proteins in milk is casein so yes this is casein. Casein is not moldable per se once it's set up it's set up but it can be mix with formaldehyde to cross-link and will harden in a mold so in that respect it is mold moldable get quality casein you have to clean all the facts out another things like milk sugars Exedra

    He can be quite difficult to do this but with a little effort it can be done to completely strip all of the facts from the case and and leave it Sterling White I have found that the only way is here's the thing ethyl ether.

    So basically you precipitate the casing out in the usual manner with acid in Hotmail rinse it with cold water strain it I use coffee filters and I've rigged up a vacuum funnel to handle a large amount vacuum it for a long long time and then put the large mass into 1000 milliliter beaker with methanol and run it in homogenizer for several hours then vacuum filter it again run clean water through it to get any remaining methanol out Andrey dissolve it using 30% ammonia hydroxide using the homogenizer on its lowest setting to get a nice dissolved case and solution. Precipitated one more time rinse it and press it and it'll be very very very clean this is the only way to get a good stable casein to make decent plastic otherwise it's crap and it will crumble in time. You can do a million things with casein there's a hundred thousand pounds out there to play with


    3 years ago on Introduction

    Ok, so I have looked through pretty much all the comments and come to the conclusion that this is NOT cheese because cheese is made with the acids produced by different kinds of bacteria. However is IS pretty much cottage cheese or paneer, both edible and very spoil-able substances. So my question is, how the heck is this not suppose to mold and go bad?? I tried it and mine molded after a couple days.

    3 replies

    Reply 3 years ago

    If you do look at the title it clearly says Homemade Plastic not how to make cheese.


    Reply 3 years ago

    If YOU do look at what she said, she clearly got that. What she got, and you clearly didn't, is that it IS more or less cottage cheese. Look it up. Some people are so quick to judge and ridicule.


    3 years ago

    It does make a good device case


    3 years ago

    It does make a good device case


    4 years ago on Introduction

    You could make capacitors with this. It will have a very high dialectric constant. If you add a bit of plaster into the mix, it will be ideal Bakelite. Bakelite Capacitors were some of the highest value capacitors around back in the day (approx. 60s).


    4 years ago

    Why is it that green stuff (those are molds, aren't they?) start growing on the one I made? Is it the amount of vinegar or milk or what??


    10 years ago on Step 5

    I play airsoft a lot and I play with some people with guns that hurt pretty bad...and this may sound weird but I was wondering if I made this thick enough do U think it could withstand some pretty hard blows like from guns shooting at 400+ fps... TYVM

    8 replies

    Reply 10 years ago on Step 5

    btw is there anything I could add to make it stronger?? And if u could e-mail me back on this I would greatly appreciate it


    Reply 10 years ago on Introduction

    well this maybe the dumbest thing i ever suggested but you could try putting pencil lead(graphite) in it it is carbon and they add carbon to steel to make it harder and fabric or something but thats just what i would try


    Reply 6 years ago on Step 5

    Steel is iron alloyed with carbon. Putting pencil lead in casein would be like putting pieces of steel in lead to make it harder. It won't be much better than it would without the graphite. Something like fabric or paper pulp could work, though, and I don't think it would set any faster. Fibers make things stronger.


    Cool Idea, But how much milk are you willing to spend on this?

    Imagine, an army of Cheese-weilding warriors!


    Reply 10 years ago on Step 5

    It might work, if you make it thick enough. It's pretty brittle in thinner layers, and as such, wouldn't do well as body armor.

    As for "making it stronger" (your note below), you could possibly add some fabric, of some sort to strengthen it.