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Mar 01

Shellac Nail Polish: How Does It Work?

by azmanam | Categories: chemical education, fun, materials chemistry | (503162 Views)

See other articles in the How Does It Work series.

Shellac nail polish, sometimes referred to as gel nail polish, is all the rage these days.  They claim to give a chip-free coating to your nails and can last several weeks.  It can last even longer than that, but after two or three weeks, your nails have grown out and you can start to see unpolished nail at the base of your polished nail.  If you go in for a quick touch up and fill in, your shellac nail polish can I guess last indefinitely!

What is Typical Nail Polish?

To start, let’s talk about typical, boring, old nail polish.  At is core, nail polish is nitrocellulose dissolved in a solvent.  Nitrocellulose is known for giving a nice, shiny, hard film once the solvent evaporates.  Nitrocellulose is also known for exploding.  It’s what makes up magicians ‘flash paper,’ and guncotton.   Fortunately, our nails don’t explode.  I’m pretty sure the manufacturers worked on figuring that one out before mass producing nail polishes.

Plasticizers and other resins are an important component in basic nail polish.  Without plasticizers, the nitrocellulose film would be very brittle and would chip and break very easily… well, more easily than it already does.  Camphor, stearate esters, other fatty acids, and castor oil are common plasticizers and resins added to nail polish.  These allow the polish to both adhere firmly to the nail and allow the polish to have some give to it so it doesn’t chip too easily.

If nothing else is added, you have a nice, clear, colorless nail polish.  If you want a colored nail polish, pigments need to be added.  Other effects can be made by adding other additives.  Micas (ground-up shiny minerals commonly used in cosmetics) or pearl essence (ground-up fish scales) or gold or silver flakes can add nice looking effects to nail polish.

How is Shellac Nail Polish Different?

Shellac nail polish must have some differences from regular nail polish.  Just on observation, it’s thicker than regular nail polish and somehow it doesn’t chip or break nearly as easily.  Plus, you “cure” it under UV light and it dries immediately.  Shellac nail polish is similar to acrylic nail polish in that they are acrylate polymers.  Shellac nail polish is a type of methacrylate polymer.

To a first approximation, shellac nail polish is a mixture of methacrylate monomers (not methyl methacrylate, that’s banned for toxicity reasons) and a radical initiator (benzoyl peroxide or some such initiator).  When placed under UV light, a classic organic chemistry reaction takes place: radical polymerization.  The reaction initiates by the homolytic bond cleavage of benzoyl peroxide to form two oxygen radicals.  These decompose further to carbon dioxide plus a phenyl radical.  This adds to one side of the methacrylate double bond, leaving a resonance-stabilized carbon-centered radical behind.  The reaction propagates by the carbon-centered radical adding to one side of another methacrylate double bond, leaving a new carbon-centered radical.  This process repeats indefinitely until all the monomers have polymerized.  The reaction terminates when two carbon centered radicals combine.

(Click for larger)

Some of the methacrylate is probably in the form of hydroxyethyl methacrylate – a protein specific monomer that will firmly attach itself to the nail plate.  This helps the polish adhere to the nail.  This, I think, is the key: Once the polymer has formed, it is quite resistant to chipping.  The polymer poly(methyl methacrylate) (PMMA) is often a shatter-resistant alternative to glass and is known as Plexiglas.  This shatter resistance is what keeps shellac nail polish from chipping over time.

Now, that was just a first approximation.  If it was actually a mixture of monomers, the polymerization would not be very efficient.  The gel is thick, and it can be difficult to get the UV light deep into the gel.  Most of the monomer would not form polymer under these circumstances.  Instead, the actual product in shellac nail polish is short methacrylate oligomers, short chains of methacrylate monomer.  If the monomer is a liquid and the polymer is a solid, it starts to make sense why the oligomer polish is a gel – intermediate consistency between a liquid and a solid.  The polymerization of these oligomers is more efficient than creating the entire polymer from the individual monomer units.

Also, because the gel is rather thick, several thin coatings must be used.  If you try to apply one thick coating and just get it over with, the UV light would hardly penetrate into the gel layer.  Keeping the layer thin makes for more efficient curing.  Several thin layers lead a better effect.

A quick wiping with isopropanol removes the sticky uncured inhibition layer on top and finishes the treatment.  To remove, since it’s a more durable polish, you need a stronger nail polish remover. The watered down acetone sold in stores won’t cut it.  You really need essentially pure acetone.  This will soften the polymer enough to allow it to be removed.

Beware

You can now buy home shellac nail kits.  You can buy home UV lamps and the shellac nail polish and do all this yourself at home.  This is really the only reason I know anything about this.  My mom loves this nail polish and bought a home kit.  She told me that one day she was enjoying a warm day on the patio and applying her shellac nail polish.  By the time she was finished, her brush was completely solidified and unusable!  Looking back, this makes a lot of sense.  If your outside, you’re in the sunlight, and the UV light from sunlight was enough to polymerize the polish left on the brush and solidify the brush.  For this reason, you shouldn’t apply outdoors.  Also for this reason, all shellac nail polish (even clear colorless ones) are sold in opaque bottles.  Definitely don’t want the polish polymerizing during transit…

Many have asked about the safety of being exposed to UV light.  You’re probably exposed to more total UV light during your trip to and from the nail salon than you are during the curing process.  Still, broken lamps or extreme over exposure will eventually lead to sunburn.

Bonus: What about Crackle Nail Polish?

As I was presenting this to my organic chemistry class, someone asked about crackle nail polish.  How does that work?  Going back to nitrocellulose nail polish, to get a nice, smooth, even film the solvent needs to evaporate very slowly.  Butyl acetate or ethyl acetate are common solvents for typical nail polish.  If you use a solvent that evaporates too quickly, the remaining solvent tends to pool together (bringing the pigment along with it) and leads to a cracked, uneven film finish.  This is, technically, a design flaw.  Unless you take your design flaw to your boss and say, “Hey!  Let’s create a market where there wasn’t one before and market my design flaw as a cool, must-have accessory for nail polish!”  Then you get a raise and a promotion.

The solvent in crackle nail polish is typically ethanol, which evaporates more quickly than the acetate solvents used in typical nail polish.  If you apply the ethanol-based crackle coat over top of a dried layer of typical nail polish, a cracked, two-toned effect occurs, leading to the crackle finish.

Extras:

  • This page has a really nice, really detailed glimpse into the chemistry and science of manicures
  • Here’s a truncated ingredient list for the Shellac system, for you structure junkies out there :)
  • Fun fact: German-Swiss chemist Christian Schönbein (1799-1868) sometimes worked on his chemistry at home, against his wife’s wishes.  One day, he spilled some nitric acid/sulfuric acid.  He mopped it up with his wife’s cotton apron and hung it up to dry.  Whereupon it spontaneously ignited and burst into flames – with almost no smoke and no ash.  He is credited for accidentally discovering nitrocellulose.  At the time (around 1845), when ordinary gunpowder exploded, it produced a thick, black smoke.  This is bad in battle for at least three reasons: 1) it gives away your position, 2) it obscures your view of the battlefield, and 3) the soot clogs up the weapon.  So the accidentally-discovered nitrocellulose was developed as a useful alternative to gunpowder.
  • Since nitrocellulose produces such a nice film (made flexible with plasticizers), it was used as the film base for early motion pictures.  It worked pretty well… except for the whole catching fire really easily part.  Projector rooms were often fitted with several layers of fire protection, sometimes directly built in to the projector itself, to prevent the inevitable fire from spreading to the auditorium and causing massive damage and casualties.
  • Nitrocellulose cinema films were used until the early 1950s when other, safer films (like cellulose triacetate) replaced nitrocellulose film.  Around the same time, chemists were discovering that nitrocellulose, dissolved together with some other resins and plasticizers, made nice, high-gloss coatings on things like metals and wood.  This allowed nitrocellulose to be used as a lacquer, and many automobiles and instruments were lacquered with fast drying nitrocellulose lacquer.  Billiard balls sometimes were also lacquered with nitrocellulose lacquer… except that the high-impact collision with other billiard balls would sometimes cause the billiard balls to explode.  In fact, many of these lacquers and early nail polishes got their nitrocellulose from dissolving old nitrocellulose cinema filmstrips.
  • Hydroxyethyl methacrylate is a common monomer (the shellac system quotes hydroxypropyl methacrylate in their ingredients list, though).  When polymerized by itself, poly(hydroxyethyl methacrylate) is hydrophobic, but is capable of absorbing from 10 – 600% water relative to dry weight and will swell.  When the properties were properly refined, the polymer was one of the first materials used to manufacture flexible contact lenses.

So there you go!  Enjoy you’re next trip to the salon and see if your manicurist will talk chemistry with you :)  If you have ideas for future How Does It Work entries, let me know!

36 comments

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  1. RB Woodweird

    Nitrocellulose turns out not to be such a good archival medium. Between its instability/flammability and lack of any preservation organization, roughly 80% of the films made between about 1900 and 1930 are lost and 50% of those made between 1930 and 1950.

  2. Dan Falvey

    Thanks! Forwarded link to my Orgo 2 students.
    Dan

  3. grubber

    yeah, nitrocellulose films, inglourious bastards! haha :)

  4. Katherine

    That’s really interesting. I may have told the girl doing my nails this morning that I would have better things to do than find out how the UV worked with the polish but I guess once a chemistry student always a chemistry student….

  5. Susana Tomasio

    Hi!
    Interesting blog!
    Have a look at mine:
    http://itsallaboutchemistry1.blogspot.com/
    Cheers,
    Susana

  6. Jasna

    I wanted to know how does crackle nail polish work and you helped me, but I still don’t understand why it doesn’t crack when you apply it directly on your nails or on other surfaces. Can you explain that? I tried to put black crackle nail polish directly on my nails and it just dried without cracking. Then I put white crackle nail polish on top of that and it didn’t crack either. I really don’t get it. :D

    1. azmanam

      Sorry, Jasna, I don’t know. I’m a dude. I’ve never actually worn crackle nail polish. Have you ever tried putting on a regular coat of regular nail polish, then a coat of crackle nail polish… then a second coat of crackle nail polish? does it crack in the same pattern as the first, or do you get a three-toned, two-cracked pattern?

      Maybe when you apply crackle directly to the nail, it adheres to the protein in the nail (which it can’t do if there’s a layer of nail polish already down). Then the second crackle coat just layers on the first? I’m guessing here.

      If you want a no-base, cracked look, you could always first put down a coat of clear regular nail polish, then the crackle coat?

      1. Jasna

        It’s not about that, I just wanted to know. I’m a girl but I almost never use those things. This was interesting to watch and friend of mine and I played with it and that raised questions. Yes, I know how that sounds. :D Thank you for your help. I’ll try sending email to the companies who make it. :)

        1. azmanam

          Keep asking great questions :) That’s all science really is! Let us know if you get a more definitive answer.

  7. Travis

    Great post! I wrote a post on the chemistry of magnetic nail polish a while ago from a patent perspective: http://www.chemicalnovelty.com/2012/01/chemistry-of-magnetic-nail-polish.html

    1. azmanam

      Thanks :) I saw the magnetic nail polish as I was researching this article. I thought it was already long enough. Now we can point readers to more information.

  8. Tia

    Fantastic! I am always curious about how things work and this information is explained well and very easy to understand. My daughter bought the crackle polish and I sit here, up early as always, wondering how the crackling works. You’ve answered my questions plus given a healthy dose of trivia! I can already see my daughters 14 yr old eyes roll when she wakes up to the Saturday morning chemistry lesson she is about to learn :) Thanks so much for the information!

    1. azmanam

      Cool, thanks for reading! How did Saturday Morning Chemistry go?

  9. I am an Infection Control Nurse in a hospital. I am trying to find out if shellac is an appropriate fingernail polish to be worn by direct patient care employees. According to regualtions… “Any fingernail enhancement or resin bonding product is considered artifical. Fingernail extensions or tips, gels and acrylic overlays, resin wraps, or acrylic fingernails constitute types of artifical fingernails.”
    Is shellac this?

    1. azmanam

      I’m not sure I’m in a position to give you a definitive answer to your question. Do you allow regular nail polish? Chemically shellac’s more like the ‘acrylic fingernails’ you list above. Since I’m a dude and don’t get my nails painted nearly often enough, I don’t have a very good answer for you.

      If you do allow typical nitrocellulose fingernail polish, what is it about the nitrocellulose polish that makes it safe, but gels and acrylics are not safe?

      Perhaps a female scientist who understands the chemistry and has more experience with ‘artificial fingernails’ can provide more insight and better answer your question?

  10. Jackie Stefan

    Question: Can I put on the Shellac base coat, then my own “non-shellac” color, THEN Shellac Top coat? hmmmmm thanks!!!

    1. azmanam

      I would guess yes, unless the ‘non-shellac’ color doesn’t adhere well to the base coat. Top coat should be ok, I’d think.

      Try it and let us know!!! :)

    2. Michelle Barrow

      I’m a nail tech… Answer to the question can you use ur own color with shellac base and top coat.. No you can’t the shellac base needs to be cured in a UV light for 10 seconds the top coat is 2 minutes. When u apple to regular coats of polish to the shellac base coat it doesn’t dry!!! U have to than wipe off the sticky coating on the top coat after it’s cured for 2 minutes so it smudges the polish because the coats of the regular polish isn’t dry. I’ve tried it at the spa I work at so we had more colors!! Hope that helped…

      1. Bev

        Reply

        As you are a nail tech would you be able to tell me why the sun has affected the colour of my uv nail polish? I had a lovely glittered deep purple colour, which is now a light lilac colour after sitting in the garden. I’m perplexed !

        With thanks
        Bev
        Wales UK

  11. lisa

    Hi who ever put the article about the Shellac ingredients, maybe you can help me…I’m a nail tech who loves using Shellac. My 10yo daughter also likes to wear it. However my notoriously trouble-making ex-husband is insisting Shellac is bad for my daughter & will make her sick? Can you shed any light into this? Are the methacrylate polymers it contains bad? I’ve been googling all night trying to find stuff, so I’d so much appreciate help!!
    Lisa

    1. azmanam

      I’m not a medical doctor, nor should my comments be taken as such, but as a chemist I’d say don’t drink them, use them as intended, and there should not be any adverse effects.

  12. ML in Mass

    Great article, thanks!

    Are you able to say what is an effective solvent for gel nail polishes? Maybe it will help if I explain my question.

    Before I put this product on myself, I want to be sure I can get it off without damage to my naturally thin nails. I have spent a good chunk of time researching this on the web (obviously, without the benefit of a PhD in Chemistry), and my findings are somewhat alarming.

    My research indicates that acetone is not truly a solvent for the cured product. Rather, it sounds like acetone softens the topmost thin layer of the nail itself, which then separates with the cured product.

    I got a home kit for Christmas, and I suppose I can run some experiments on, say, an old butterknife, and then see if acetone, lacquer thinner, or will work.

    This is haphazard–emphasis on the ‘hazard’ part. I’d rather have the opinion of someone who can report, oh yes! methyl cellulose (furniture stripper) will work! NOT that I would use it on my body, I’m just trying to add some humor here.

    Also just want to say I am many, MANY years out of high school, but your article brought me back to the classroom of my high school chemistry teacher who made me love the subject then. Thanks. –ML

  13. Carol

    What is the relation between that shellac, and this shellac: Shellac – Resin secreted by lac bug (Kerria lacca)?

    1. Doug Schoon

      Hi Carol,
      There is NO relationship. Shellac is a marketing brand name. This product has nothing to do with the lac bug.

  14. Doug Schoon

    MessageI wanted to correct a few factual errors in this blog. For example, Methyl methacrylate monomer (MMA) was not banned for toxicity reasons. It is used all around the world for dental prosthetics, contact lenses, and is even implanted into the body as a bone cement, so the effect of exposure to humans is well understood. MMA is NOT considered to be a cancer-causing agent nor does it damage unborn fetuses, so all the myths you state here are nonsense. It does not make a very good artificial nail because it is too hard to remove and should not be used, but again, not because it is “too toxic”. You are also in error to suggest that Shellac contains, BPA. It does NOT! Isopropylidenediphenol has never been an ingredient in this product. You also incorrectly suggest the product contains PMMA. This may be because you have interspersed general nail product information with specific product information. In order to avoid confusion, it would be best to separate the two kinds of information.

    Finally, you are using the term Shellac improperly. Shellac is NOT a generic term. It is a specific brand name of UV curing nail polish. It’s the most popular and widely used, which may have confused you. Even so, there are no “home Shellac nail kits”. Shellac is to be used by trained nail technicians in the professional salon setting.

    You are correct that these UV nail lamps are safe. They’ve been tested by one of the world’s leading researchers and experts in UV and skin exposure and inventor of the SPF rating system, Dr. Robert Sayre. Dr. Sayre’s paper, which will be published Spring 2013, will verify the safety of these lamps.

    1. azmanam

      @Doug:

      Thanks for your comment.

      I think you may be confusing the monomer methyl methacrylate (MMA) and the polymer poly methyl methacrylate (PMMA). According to several websites (1, 2, 3 (page 7), 4 (MSDS)), MMA is toxic and has been banned in several countries. Poly methyl methacrylate (PMMA), on the other hand), will not have the same properties as MMA and is probably non toxic when used in dentistry, cosmetics, or bone implantations.

      I also think you may have them confused because you say MMA would make a good artificial nail because it is too hard to remove. MMA is a liquid. It would make a bad artificial nail because it is a liquid. PMMA, on the other hand, is sold under the brand name Plexiglas and I agree would be quite hard to remove.

      You are correct, BPA is not an ingredient. It is listed on all three data sheets linked above (base coat, color coat, top coat), but as part of the larger molecule “isopropylidenediphenol PEG-2 dimethacrylate.” I missed the fact that there wasn’t a comma separating this into two ingredients (which is how I originally read it). Thanks for bringing this to my attention.

  15. Emily

    Do you even know who Doug Schoon is?! I really don’t think you should be questioning his knowledge with regards to nail chemistry…

    I suggest you google him :)

  16. Shellac Nail Polish

    Great tips here! I know its an old blogpost but still thanks for sharing your insight. Its very inspiring also for us girls at http://buyshellacnailpolish.com I do not mention it to spam or advertise but really do mean it.
    We might also host some of your videos at some point and of course mention your site.

    Ivon.

  17. Katya

    Hi! So, is Shellac actually flammable or not? Is it safe to mail internationally? I know that regular nail polish is prohibited… Would Shellac be different? Thanks!

  18. Jacqueline McCarthy

    Hi there

    I am an anaesthesiologist working in the UK. I am writing a short article about shellac and the effect it can have on pulse oximetry monitoring. I have been trying to find out a little about its chemical structure and your blog is the best description I have been able to find. I would be keen to use your description in my article and obviously provide full credit for your input. Would I be able to quote you in my article and how would you like me to reference your excellent decription?

    Many thanks

    Dr Jacqueline McCarthy

    1. Christel

      Dr. McCarthy,

      My question to you is related to Shellac but not in regards to pulse oximetry. I am wondering if you have any information on whether or not Shellac poses an increase risk of infection to our patients. Many hospitals allow Shellac polish to be worn but many do not. The information I have found is inconsistent. Wondering if you could shed any light on this as the hospital I am working at does not allow Shellac to be worn but will allow regular nail polish. To me it seems it should be the other way around as Shelllac holds up longer without cracking or chipping and is removed completely prior to reapplication unlike acrylics or gels.

      I appreciate your thoughts!

      Thanks!
      Christel Burke CRNA MS

  19. Callyce Tucker- Reves

    Hi, I am a STEM reprehensive for Maxson Middle School, I am doing a competition called e cyber mission. My team and I are doing an experiment and the experiment is that we are trying to make nail polish odorless. If you have an please contact me.

  20. Jennifer Booth

    can I use Shellac found in hardware stores for my base and top coats?

  21. Katie Hughes

    Thanks for that – great article! I tried CND Shellac for the first time recently and loved it. I’m not a chemist in the slightest, but was interested to know why the product has to be cured under UV and what the chemical reaction was that takes place to make it shiny and non-cracking. Now I know! Brilliant, even for a non-scientist. Thank you! x

  22. Michelle

    Hi, I would like to formulate a gel nail polish that would not need curing by UV or LED. I am currently doing formulation science and have a diploma in polymer chemistry which is really fun. I haven’t done any research as yet and this is what I first came across. Can this be done? Is it advisable?

  23. Christine

    Thank you for the information. Are yo able to provide the name of the shellac polish that your mother uses? I would like to purchase a reliable product for at home use.

    Christine

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