Science shows that certain smells trigger memories in our brain. For instance, grass may remind you of playing outside as a kid, or freshly baked cinnamon buns could bring flashbacks of working at Cinnabon as a teenager.

Highlighters work the same way! Their chemical smell may just spark memories of being in school. So what exactly is inside of highlighters that gives them their scent? Also, why do they never seem to run out of ink? It’s time for a quick chemistry lesson!

What Ingredients Are in Highlighters?

Most highlighter ink contains fluorescein, which is an organic compound and dye that is soluble in water. The tip, on the other hand, is made from polyethylene or polyester beads, both of which are lightweight types of plastic.

Although most highlighters use fluorescein to get that neon hue, the other ingredients will vary. It just depends on which color is being created.

The following chemicals may be found in highlighter ink:

  • Fluorescein
  • Pyranine
  • Triphenylmethane
  • Rhodamine
  • Xanthene
  • Coumarin

Pyranine

This chemical compound is primarily used to make yellow highlighters, but surprisingly, it’s also been found in different types of soap!

Triphenylmethane

You can’t go wrong using a highlighter made from triphenylmethane. It will produce a blue ink that stands out in your notes or textbooks.

Rhodamine

Rhodamine is a chemical that’s used to dye paper and ink. It’s mixed with triphenylmethane to create pink or purple highlighters.

Xanthene

With its yellowish color, xanthene is an excellent chemical to use in highlighters. It’s mixed with another chemical known as coumarin to create orange ink.

Coumarin

It might be surprising, but coumarin is totally colorless and has a vanilla aroma. This chemical compound is mixed with xanthene to create orange highlighters.

Why Are Highlighters So Bright?

You probably think of the word “fluorescent” when you think of highlighters. This comes from the main ingredient in the ink, fluorescein, which is naturally a lot brighter than other chemical compounds.

Fluorescent ink absorbs and reflects more light than other types of ink. This is why your black ink or red ink pen appears more subdued, while a highlighter’s ink seems to glow.

Fluorescent ink is also used to make construction equipment, cones, and safety vests.

How Are Highlighters Made?

Highlighters seem to magically never run out of ink, which is in large part thanks to the way they’re made. The process is designed in a way that ensures the ink is thick and full of moisture.

This is how a highlighter is created step by step:

  • Step One: A vacuum siphons plastic pellets into a large container. These are dyed in the eventual color of the highlighter’s barrel.
  • Step Two: The plastic pellets are heated and melted down into a liquid form at about 240°F.
  • Step Three: A mechanical steel screw pushes the liquid plastic down into premade pen molds.
  • Step Four: The highlighter barrels are cooled down by water and stored in a container.
  • Step Five: On a separate conveyor belt, chalky pieces of polyester are pushed into clear pen barrels. This will eventually be the ink.
  • Step Six: A chemist drops a concentrated amount of dye into a beaker of water. This water contains a humectant, which allows the ink to retain its moisture for an extended period of time.
  • Step Seven: A metal probe is used to measure the thickness of the ink. It has to be just right in order for the ink to be used.
  • Step Eight: Mechanized needles are used to inject the ink into the polyester pieces.
  • Step Nine: The highlighter tip, or nib, is added to the top of the clear pen barrel. The ink will flow out of this piece.
  • Step Ten: The highlighter caps are moved down a conveyor and added on top of the nib.
  • Step Eleven: Screen or pad printing is used to add a logo or text onto the highlighter barrels.
  • Step Twelve: The highlighters are ready to be shipped to suppliers.
  1. Step 1
    youtube.com

    Siphon the Plastic

    The first step involves siphoning plastic pellets into a large tube. Half of the pellets are white and the other half are dyed in the intended color of the highlighter.

  2. Step 2
    youtube.com

    Melt the Plastic

    The tube that holds the plastic pellets is heated at about 240°F, which causes them to melt into a liquid form. As it all melts together, the colorful pellets will overpower the white ones, ultimately creating the ink color.

  3. Step 3
    youtube.com

    Push Into Molds

    A mechanical steel screw pushes the liquid plastic into premade pen molds. The pressure at this point is equal to the weight of 350 elephants!

  4. Step 4
    youtube.com

    Cool Down the Highlighters

    The highlighter barrels are cooled down by water and stored in a container. Without this step, the highlighters would be too hot to touch and wouldn’t be able to go on to the next stages of manufacturing.

  5. Step 5
    youtube.com

    Push in the Polyester

    Clear pen barrels are pushed on a conveyor belt, while chalky pieces of polyester drop down on a separate conveyor belt. A robotic arm then pushes the pieces of polyester into the clear pen barrels.

  6. Step 6
    youtube.com

    Drop in the Dye

    A chemist uses an eyedropper to drop a concentrated amount of dye (usually between 10 and 20 drops) into a beaker of water. This water contains a substance known as a humectant, which allows the ink to retain its moisture. It’s for this reason that highlighters don’t run out of ink very quickly!

  7. Step 7
    youtube.com

    Measure the Ink’s Thickness

    A metal probe is dipped into the ink. It’s connected to a gauge that measures the thickness of the ink. If the probe turns too fast, it means the ink is too thin. If it’s too slow, the ink is too thick. It has to be moving at just the right speed in order for the ink to be used in the highlighter.

  8. Step 8
    youtube.com

    Mix the Ink with the Polyester

    A robotically operated needle is used to inject the ink into the chalky polyester pieces from Step Five.

  9. Step 9
    youtube.com

    Add the Nib

    The tip, or nib, of the highlighter is added to the top of the clear pen barrel. This is where the ink flows out as you’re using the highlighter.

  10. Step 10
    youtube.com

    Screw on the Cap

    The highlighter caps are moved down a conveyor and added to the top of the nib.

  11. Step 11
    youtube.com

    Print a Design

    Screen or pad printing is used to add a logo or text to the highlighter’s barrel. This is usually a brand name like Sharpie or BIC, but it can also be a unique design.

  12. Step 12

    Pack the Highlighters

    The highlighters are now good to go. They are packed into boxes and shipped in bulk to stores or online retailers. Demand is usually very high during back-to-school season!

See the entire process in action by watching this video!

Highlighters are water-based instead of alcohol-based in order to prevent the ink from seeping through the paper.

How Much Ink is in a Highlighter?

On average, a highlighter will have about 10 ml. (0.33 oz.) of ink. This will give you approximately 50,000 words you can highlight before you have to worry about it drying up. It’s no wonder why it seems like highlighters never go bad!

How Should Highlighters Be Stored?

You should store highlighters upside down with the cap on top. This ensures that the ink won’t dry out quickly, and the highlighter will last for a longer period of time.

The following are great places to store your highlighters:

  • Cup or mug on your desk
  • Mason jar in your kitchen
  • Pencil case that you keep in your bag or backpack
  • Junk drawer
  • Plastic tub with a lid on top
  • Wicker or cloth basket in your office
  • Makeshift shelf on a corkboard

Cup or Mug

Keep your highlighters in arm’s reach by storing them in a cup or mug on your desk. Choose a fun pattern or color, and you’ll instantly brighten up your workspace!

Mason Jar

If you want to start planning your meals, keep a mason jar full of highlighters and pens in the kitchen. Create a calendar and use one color for breakfast, one for lunch, and one for dinner.

Pencil Case

Zippered pencil cases are a great way to keep your highlighters and other supplies organized. You won’t have to sift through the bottom of your backpack again!

Drawer

Every house should have a junk drawer! This is where you’ll keep odds and ends like rubber bands, pens, scissors, and of course, highlighters.

Plastic Tub With Lid

You might already store your craft supplies in storage containers. Consider doing the same thing for office supplies, such as notebooks, pens, and highlighters.

Basket

Wicker or cloth baskets are a must in every household. They look elegant, but also work wonders at hiding any unwanted clutter. Leave a few in your office to hold your highlighters and other supplies!

Corkboard Shelf

Create a DIY shelf by pushing two push pins evenly apart on a corkboard. Then you can simply rest your highlighter on the top!

Being organized is said to increase your productivity. With that in mind, it’s worth brainstorming ways to declutter. Start with your office supplies and then go about organizing everything else. You won’t regret it!

https://www.coolthings.com

Do Highlighters Fade?

Most highlighters will not fade over time! The ink is permanent, which means the mark won’t go away. Keep that in mind if you don’t want to ruin the pages in your favorite novel.

Do you want a highlighter with fade away ink? Try the Fader! This marker features ink that will disappear after just five months. It’s an especially great option for students who want to mark passages in their textbooks without anyone knowing about it!

Are Highlighters Toxic to Humans?

Highlighters are made with chemicals, so it may be dangerous to ingest the ink. If you, your child, or your pet accidentally consumes any toxic materials, reach out to poison control at 1-800-222-1222.

The Bottom Line

Fluorescein, and other chemicals like pyranine and rhodamine, are almost everlasting. Your highlighter marks won’t fade away, even after a few years! So give a silent “thank you” to the folks that make these bright pens. Studying, meal calendars, and projects at work wouldn’t be the same without them!

References

How It’s Made. (2008, July 9). How It’s Made – Highlighters. Retrieved from,
https://www.youtube.com/watch?v=ogezywfzDa0

Cheddar Gadgets. (2019, October 30). How Highlighters Are Made. Retrieved from,
https://www.youtube.com/watch?v=xmOqVUKlQww

Compound Chem. (2015, January 22). The Chemistry of Highlighter Colours. Retrieved from,
https://www.compoundchem.com/2015/01/22/highlighters/

Lu, A. (2019, February 14). How Long Does it Take the Average Highlighter to Run Out of Ink? Retrieved from,
https://blog.123ink.ca/2019/02/how-long-does-it-take-the-average-highlighter-to-run-out-of-ink/

How It Works Daily. (2014, July 2). What Makes Highlighter Pens So Bright? Retrieved from,
https://www.howitworksdaily.com/what-makes-highlighter-pens-so-bright/

Smith, S. (2017, February 1). 7 Household Items You’re Better Off Storing Upside Down. Retrieved from,
https://www.rd.com/list/items-store-upside-down

About the author

Alyssa Mertes

Alyssa is a promo expert with over four years of experience in the industry. She is the Lead Copywriter at Quality Logo Products and has had work published for the Promotional Products Association International and the Advertising Specialty Institute.