HUMIDITY TANKS

 Humidity is one of the most overlooked parts of pressing and preserving comics, and it can make or break your results.  Paper is organic. It breathes, absorbs, and reacts to the air around it. If your pressing room isn’t stable, you’ll fight against nature every time you press. A comic won’t just remember folds and creases—it will “remember” the environment it was stored or worked on in.

· Temperature Range (70–75°F)

The 70–75°F range is considered a sweet spot—comfortable for you, stable for all comic  books. “Comics want to be comfortable, like people.”

     o Too hot: Paper fibers become brittle over time, inks can fade faster, and press heat has less predictability.

     o Too cold: Paper stiffens and becomes less flexible, making it harder to “relax” during pressing. Flaring is a common side effect to a cold room.

· Humidity Range (40–50%)

At 40–50% relative humidity, the paper fibers stay flexible without swelling—perfect for pressing.

     o High humidity (above 55–60%): Paper absorbs moisture and swells. Glossy covers can wrinkle or ripple (called humidity waves). Mold can develop inside boxes and books. Pressing results won’t hold—creases you flattened can “reappear” once the paper reabsorbs moisture.

     o Low humidity (below 35%): Paper dries out and becomes brittle. Staples and inks can expand/contract differently, causing stress marks. Waviness is a common side effect to a low humidity environment.

BENEFITS OF HUMIDIFICATION

There are several websites available online that mention the benefits of humidification to paper, including the Library of Congress.  According to the National Park Service,  “Paper records such as maps, newspapers, and documents that have been rolled or folded for long periods of time often may be safely flattened using carefully controlled humidification. There are three basic steps to humidification: cleaning, humidifying, and weighting or flattening. Each step requires somewhat specialized equipment that can be easily constructed from materials gathered from common sources, such as hardware and fabric stores. Extreme care must be used when initially opening papers that have been folded or rolled. While some papers remain supple over time, others may grow increasingly fragile due to inherent weaknesses, widely fluctuating temperature and relative humidity, or exposure to light and/or to chemicals in the atmosphere. As a result, paper remembers creases, folds, and curls. If records are not flattened carefully, they may crumble, and their valuable Information will be irretrievably lost. Never attempt to open a rolled or folded piece of paper if you are uncertain of its physical condition, particularly if the climate is extremely dry (less than 35% relative humidity)."

STORING PRESSED BOOKS

Keep all pressed books for 7 days until they are sent to a grading company or client.  Keep books in the same pressing room.  Keep all pressed books closed inside a bag and board.  If you must stack books, do so in a manner that is stacked cover to cover, tape to tape, alternating sides, inside an airtight letter-sized  plastic hard shell storage container.  After 7 days, perform a reversion inspection and check your edges.  Take new “before and after” photos, to compare results.

DISTILLED WATER

Previously it was stated in the original 2019 Comic Book CPR that “Distilled water is the only type of water that should be used for humidity.  Minerals and other impurities have been removed during processing.  This prevents tide lines and water staining if there is excessive moisture or droplets.”  However, we have seen no evidence in almost 10 years that tap water contributes to mineral deposits on book covers.  You are free to use tap water, bottled drinking water, or distilled water for your humidity tank. 

CHECK YOUR EDGES

Too much humidity is often permanent and irreversible damage to comic books.  This is a very delicate process and should be used in a conservative manner.  Flaring, warped covers, cockling, rippled pages and spine splits can result from the oversaturation of paper.  After pressing, all comic books should be super flat and straight at both the top and bottom edges.  If the edges are wavy, the paper fibers expand too much from oversaturation.  An extended two-day cold press may be necessary first, prior to regular pressing, to dry out paper fibers into a more relaxed state, which will produce flat and straight edges.   Another cause for the waviness is simply pressing books in a pressing room that is not under the required conditions of 70-75F and 40-50%.

MOST OF THE DAMAGE IS ON THE COVER

For most comics, the pressable defects will be mostly on the cover at surface level. The only reasons this would not be true are spine rolls, stacking curls, multiple cover books, polybagged comics, subscription creased comics, or heavily creased throughout whole book. Due to the most pressable defects being on the covers, you will likely always focus on dent removal from the covers. 

KNOW WHEN AND HOW MUCH HUMIDITY TO USE

Modern age comic books made today with glossy paper are very forgiving under heat and do not require much humidity. 15 minutes in the humidity tank may still be used on glossy modern age comic books. Vintage comic books with heavy creasing and denting would benefit more from spending at least 30 minutes to 1 hour in the humidity tank prior to pressing.

MAKE YOUR OWN HUMIDITY TANK 

The second most important piece of pressing equipment next to your press machine is a Humidity Tank.  You will learn how to make your own Humidity Tank from home.  In a nutshell, the process is very simple: you place a comic book inside a storage bin.  This storage bin has an elevated platform above a 1”-2” water table at the bottom.  After a short period of time, the book is removed from the humidity tank for dent removal and comic pressing.  The Humidity Tank should be emptied and wiped down every 7 days to prevent mold and mildew from forming inside the tank.  It is not recommended to place any mold or mildew cleaner inside your tank when comic books are present.  Mold and mildew cleaner is simply unnecessary.

HUMIDITY TANK SUPPLIES LIST 

All materials can be purchased in the kitchen department of your local retail store or on Amazon.   There are many different variations, and they all work the same way.  The main variable is how much boiled water is poured into the bottom of the tank.  As long as the water line is 1” to 2” from the bottom of the tank, all recommended durations remain constant.   Making a humidity tank is very simple and effective:    

• 40 qt Storage Tub 

• Chip Clips 

• Hot water

• Hygrometer

• Latex gloves 

• Magazine-sized backer boards

• Magazine-sized comic bags

• Metal or plastic cooling rack (16x10)

• Felt, towels, or paper towels

• Spacers (4x) (PVC pipe couplings, cups, etc.)

It’s quick and easy to assemble your very own humidity tank (some call it a humidity chamber) from home. Durations vary based on the type of paper stock and thickness.  For Modern Age magazines and giant-sized comic books with glossy thin pages, the duration is cut in half by 50%.  

Follow these simple instructions to introduce controlled humidification to comic books: 

Paper absorbs moisture like a sponge: Comic book paper is porous, so it pulls water vapor from the air. If the book is in the tank too long, it doesn’t just “relax the fibers”—it keeps soaking it in.

Oversaturation: The paper fibers swell, making pages feel soft, limp, and sometimes even “spongy.” This is what a book looks like when it is oversaturated.

Waviness / cockling:Extra moisture causes pages and covers to warp with ripples or waves. These can be hard (sometimes impossible) to fully flatten back out.

Increased fragility:The more swollen the fibers get, the easier they can tear, especially around staples or existing spine stress.

Mold risk: If the book sits too long in a damp, sealed space, mold can start forming in as little as 48 hours—especially if the tank is warm.

Safe Timing (General Rule of Thumb)

Most collectors only leave a book in a humidity chamber for 30 to 60 minutes, depending on the tank setup and the book’s paper stock. Giant-sized and magazine-sized comics require longer durations.

Anything longer than 4 to 6 hours causes oversaturation.

Thin, modern glossy comics with magazine-style paper stock absorb humidity faster than thick, older newsprint books—so always adjust timing based on the paper type. This is why we recommend 15 minutes.

Think of humidity treatment like boiling pasta—you want it just cooked enough to make the paper flexible, not soggy. If you “overcook” the paper, you can’t go back.

Early Signs of Oversaturation

· Pages feel limpinstead of crisp

· Normal paper has a little “snap” when you turn a page. If it starts feeling soft, floppy, or heavy, that’s a red flag.

· Waviness forming at the edges

· Look at the page edges—if you see ripples or cockling (like tiny waves on water), the paper has already taken in too much moisture.

· Cover loses its stiffness

· A comic cover should hold some firmness. If it feels droopy or doesn’t support the book well, it’s been in too long.

· Staple areas swell

· Check around the staples—oversaturated paper puffs up there first. If you see bulging or softening, pull the book immediately.

· Surface sheen changes

· On brand-new glossy thin covers, moisture can dull the finish or make it look slightly hazy. This means the top layer is absorbing humidity. This is also what happens when you lightly steam the cover using a steam gun to remove wrinkles.

Advanced Signs (Damage Starting)

· Spine tears widening  Swollen fibers push on stress points.

· Pages stick slightly  Too much moisture makes them tacky.

· Musty smell  Early warning of mold growth.

Rule of thumb: if you see any of the early signs, it’s time to remove the book, let it rest in a clean, dry environment, and only then decide if it needs more treatment.

 The optimal moment for dent removal is immediately after the humidity tank for tack iron or ball bearing dent removal procedures. The cover is super malleable during this phase. 

Comic Book CPR: First Edition is a giant 388 page comprehensive beginner’s guide to cleaning and pressing comic books, written for collectors who want to improve grades, eye appeal, and long-term preservation without relying on third-party services. The book walks readers step by step through inspection, dry cleaning, humidity control, pressing techniques, defect identification, and risk avoidance, using clear language, full-color photos, charts, and real-world examples. Designed to help readers recognize pressable versus unpressable defects and avoid costly mistakes, it provides a practical foundation for safely improving comic books at home while protecting their collectible value.