WARNING: IF YOU ARE USING NICOTINE, PLEASE BE CAREFUL. IT IS HIGHLY TOXIC AND CAN BE FATAL. MAKE SURE YOU HIDE AND SECURE YOUR NICOTINE FROM CHILDREN AND PETS (AND ANYONE THAT IS UNAWARE)

this is the second time i'm posting this...Steemit ate my first try for no reason :(

Yes It Is True

You can make your own e-liquid (I was calling it e-juice before, but it seems like people also use e-liquid and vape juice, so I'll try to use all three interchangeably so more people know what I'm talking about) for vaping--it's easy, much cheaper than buying pre-mixed e-juices, and gives you more control. In some cases, you might have to mix your own, just to be able to vape comfortably or to comply with local laws or whatever circumstance you're in that precludes buying pre-mixed vape juice.

For example, some people are allergic to PG (propylene glycol), which is a typical component of nearly all e-liquids. Reducing or possibly even eliminating PG altogether in your e-juice. Or maybe you're in foreign country, one which does not allow the sale of e-liquids containing nicotine, as I once was. That would be a painful discovery if you weren't prepared. And even if you were able to get around these situations by obtaining specialized e-juices from suppliers that provide custom-made products, it would still cost many, many times the amount paid compared to mixing your own vape juice.

Money, Money, Money

Is it worth the convenience of buying pre-mixed e-liquids? It might be, but you'd need to know how much more are you paying for pre-mixed in the first place. I'll present some hypothetical calculations so you can see for yourself.

Typical Cost of Buying 480 mL of E-Juice

30 mL bottle from the store = $10 - $20
30 mL * 16 = 480 mL
480 mL = $160 - $320

Typical Cost of Mixing 480 mL of E-Juice

PG 240 mL = $5
VG 240 mL = $5
100 mg Concentrated Nicotine $6
Flavor Concentrate = $4
= 480 mL = $20

As you can see, you end up paying about eight to sixteen times more for pre-mixed e-liquids! To be more accurate, that's closer to eight (maybe less during sales or for particular brands) times for online stores, and closer to sixteen times for brick-and-mortar retailers. Personally, I can go through 30 mL to 60 mL in a week or two at most. It might not be much of a difference if you don't vape constantly (like I do), but extra money is always good, right?

What You Need to Make Your Own Vape Juice

Almost all e-liquids are made of PG (propylene glycol), VG (vegetable glycerin), nicotine, and some flavors, so why would customization make a big difference when there's just four ingredients? In a way, since there are only four variables, it makes sense to assume that a change to a single one would result in a significant difference. (I'm correct in thinking that, right?). Anyway, even if it's not necessary, it can be fun to try your hand at mixing, and you might be able to create something better than what's offered at the store. So I'll go through each ingredient, briefly describing them and detailing the effects of their changes in the composition of your e-liquid.

Ingredients

PG (Propylene Glycol)

Propylene Glycol is a synthetic compound, C3H8O2 (I don't know how to do subscript in Steemit). It's basically colorless, doesn't really smell or taste like anything, and isn't very thick. You've probably come into contact with it at some point, as it's found in food products (like in preservatives), pharmaceuticals (including asthma inhalers), and in a wide range of many more products. The FDA considers PG safe, though personally, I wouldn't take their word for anything. However, their opinion is confirmed by long-term studies on the effects of inhaling PG conducted on animals which showed "no substantial risk from inhaling PG, even in high concentrations. There may be irritation and other minor effects, but overall it isn’t very harmful to mammals or other primates." [1]

VG (Vegetable Glycerin)

Vegetable Glycerin is all-natural liquid, and is usually made by extracting the oils from coconut, palm, or soy. Like PG, it's clear and doesn't smell, but is a little sweet and much thicker. VG is also very abundant in many different products we use, especially cosmetics and food products. Again, the FDA has labeled VG safe, but I would always try to get additional confirmation from other sources. So this is from the SIDS Initial Assessment Report, "The weight of evidence indicates that glycerol is of low toxicity when ingested, inhaled or in contact with the skin."[2]

Nicotine

I'm not sure this requires much explaining, but I'll mention a few things that new vapers might be unaware of. Because it's so convenient and accessible, newly-converted vapers can easily vape much more than they smoked. So it's possible to be taking in much more nicotine than they're used to, possibly resulting in nausea, headaches, stomach aches, or diarrhea. Obviously, if this is the case, then slow down! On a related note, if they're trying to get off nicotine as well, then they should remember that they are in complete control of how much nicotine goes into their e-liquids. The throat hit is also affected by the amount of nicotine, so lower the amount if the sensation is too strong.
And because it's important, this deserves it's own paragraph. Nicotine can be dangerous, especially when concentrated, so BE CAREFUL. Be careful when opening its container, be careful when adding it to your e-juice, be careful when storing, always be careful. If you get it on your skin, you won't die, but please wash it off quickly.

Flavors

The flavoring that goes into e-liquids should be studied more, in my opinion. I think that many of the flavors available were created with the intention of being orally ingested, so data on their effects when inhaled is not as thorough as I'd like. But I have to assume that the vast majority of flavors are still much healthier than smoking cigarettes, so I haven't looked into it very much. I will point out that diacetyl, a compound that produces buttery flavors, is suspected to be harmful and could be responsible in causing a condition called "popcorn lung". However, many people probably don't know diacetyl has been a common ingredient in cigarettes for decades. Additionally, most reputable companies have eliminated diacetyl from their vape juices. So do your own research, but I will say that I personally will avoid buttery flavors for now, until I am more certain.
In terms of mixing, the only advice I have is to err on the side of caution and to add less rather than more when uncertain. This should be common sense, since it's really easy to add more flavoring, but probably not feasible for most to remove it when there's too much. Also, keep in mind that the flavors can change over time, some for better and some for worse. This is also at the center of the controversy over "steeping" e-juices, generating endless debate on how much of an effect it has and even whether it is necessary or not. Again, do your own research, but even in my limited experience, it seems clear that steeping does actually improve, and may be necessary, for at least some flavors.

Equipment

Gloves

I recommend using gloves regardless the stage preparation you're in. I know that PG, VG, and the flavorings are most likely harmless, but it's good practice, and good just in case. Plus, you should have them on when handling nicotine anyway, so why not?

Syringes

You'll need marked syringes, probably some 10mL syringes for the PG and VG, and smaller 1mL syringes for the flavor concentrates and nicotine. Make sure they work well with the particular viscosity and container of each liquid. For example, since VG is thicker, you might want to use a larger gauge syringe than you use for the PG, or like, if the bottle of nicotine you have is long and thin, make sure your syringe is long enough so that you don't need to risk tilting it on its side to draw out, stuff like that.

Bottles

I've been using old bottles from finished vape juices, and really only a few recommendations. Since nicotine and some flavors can break down when exposed to air/heat/UV, I prefer glass. I also assume that glass is more chemically inert compared to plastics (I have no idea if this is true, it just makes me feel better). Though the plastic bottles are usually easier to handle when dispensing, so you might want to try both before you decide.

Ratio of PG & VG and How it Affects Vaping

While there are people on both sides of the spectrum, people who vape 100% PG and people who vape 100% VG, most (including myself) will vape with an e-liquid with a PG/VG ratio in between those extremes. Although, I have vaped solutions (I wouldn't even consider it vape juice at that point) of almost 100% VG, and can say that it acceptable, though only in the absence of alternatives. What aspects of vaping are affected as you change the ratio? The most important are: rate of absorption by the wick, strength of throat hit, quality of flavor, and cloud production.

Absorption Rate

The rate of absorption isn't doesn't usually register for most vapers, but it does make a difference if you're higher on the VG-side of the ratio. Some tanks allow you to adjust the juice flow, and you'll want to open those up as you increase the proportion of VG in your mixes. Also, after you install new coils/wicks, you need to saturate them with e-juice before vaping, so e-liquids that are higher in VG will require more time to fully soak in.

Throat Hit

For transitioning ex-smokers, the throat hit is actually pretty important. When I first switched to vaping, I would take much longer and harder hits than necessary, as I tried to replicate the sensation of the smoke hitting the back of my throat. If you're having the same issue, you might want to try increasing the proportion of PG in your mixes, which contributes much more to the throat hit than VG. But keep in mind, voltage and amount of nicotine are also factors that affect the throat hit. The opposite is also possible, as I've heard of vapers complaining of too much throat hit, so adjust accordingly.

Flavor Quality

The affect that the PG/VG ratio has on flavor is somewhat counter-intuitive. I would've thought that VG would result in more flavor due to the density, but the opposite is true. PG is a much better carrier of flavor, so more of it will result in high flavor intensity. Additionally, VG is naturally a little sweet, so more of it will result in greater flavor distortion. If you're going for sweet flavors, then it might not matter too much, but is more of a factor if you're going for savory flavors or are attempting to accurately replicate a very specific taste. I usually vape pretty sweet flavors, and don't really chase flavor anyway, so this might be why I'm okay with very high VG blends.

Cloud Production

In my experience, cloud production is the aspect of vaping that is most strongly influenced by the proportion of PG/VG in your vape juice. It might seem strange to non-smokers/non-vapers to care about how much or how thick the clouds produced are, but for some reason, it just does. I enjoy exhaling thick, billowy clouds--it's just so satisfying to see. And in certain situations, it might really matter, like if you're trying to sneak-a-vape discreetly in a bathroom or if you need the thickness to highlight your vape tricks.
There are a few other considerations, though most vapers aren't typically aware or bothered by them. One is the affect on battery life, as VG tends to draw more from the batteries compared to PG, due to the difference in viscosity. Another is the build-up of residue in your tank and on the coils, which VG is supposed to produce more of (as well as certain ingredients in different flavors), though I haven't noticed a huge difference.

Additional Considerations

There are a few miscellaneous observations I've made that have helped me out, so I'll list them here.

1

Using an e-juice calculator is much easier (and safer) than doing the calculations by hand. Just Google and find one you like. While you're at it, you can also look at similar recipes and people's recommendations for them--it could save you a lot of experimentation.

2

My friend has a "system" (not really a system, more of habit, but anyway) that he uses when mixing, which really just consists of one step: add the nicotine first. While it's simple and might not seem worth mentioning, I think it's a good idea. It's the only ingredient that would result in a catastrophic failure if accidentally added twice or omitted, so this "system" prevents that.

3

Steeping is the process of letting a fresh batch of vape juice settle, or mix, or otherwise induce a change in the flavor, rather than immediately vaping it. I'm aware that there's tons of debate on this issue, but in my experience, it makes a difference, and turns some flavors from disgusting to tasty (apple pie a la mode). Steeping can be done by storing the new batch in a dark, cool place for a while, or by introducing a little heat, but I recommend trying the first method if you're just experimenting, since other ingredients in your e-juice may deteriorate in heat.

4

When you buy flavor concentrates, they should have a recommended percentage range somewhere on the bottle. I'd try the low end of that range first, because ruining a mix is a big waste of ingredients, and it's no big deal to add more if you need to.

That's all I have for now, and I'll post more if I think of anything else.

Have fun mixing your own vape juice and have fun with the extra money you'll have saved!

WARNING: IF YOU ARE USING NICOTINE, PLEASE BE CAREFUL. IT IS HIGHLY TOXIC AND CAN BE FATAL. MAKE SURE YOU HIDE AND SECURE YOUR NICOTINE FROM CHILDREN AND PETS (AND ANYONE THAT IS UNAWARE)

Sources:
*all images labeled for reuse

1. https://www.ecigarettedirect.co.uk/ashtray-blog/2016/02/propylene-glycol-e-cigarettes.html
2. http://www.inchem.org/documents/sids/sids/56815.pdf
3. https://www.misthub.com/blogs/vape-tutorials/76788613-tutorial-propylene-glycol-pg-vs-vegetable-glycerin-vg-e-juice
4. https://en.wikipedia.org/wiki/Propylene_glycol
5. https://en.wikipedia.org/wiki/Glycerol
6. http://blog.mtbakervapor.com/the-truth-about-diacetyl/