What's Celluloid?

Let’s talk about celluloid.

As a chemist I get requests for some treatment to stabilize, even reverse the degradation, collectors experience with celluloid-handled knives.   But it’s a bigger problem than you think. 

When celluloid first became available the artistic community, always in search of a new media to work in, became enamored with it.  Celluloid had a lot going for itself.  It could be dyed, pigmented, carved, shaped, molded, stamped, printed, spattered, painted… the list goes on.  Most of these works are slowly and irreversibly decaying and will be lost forever.  Knife handles are not unique, but there are steps you can take to reduce the rate of decay. This is a job for conservators and not a chemist.  Still, I speak some of the language of conservators, so let’s talk about celluloid.

It may have started with the Big Bang, but we can start with Christian Friedrich in 1846 Europe.  He discovered cotton could be treated with sulfuric and nitric acids to make nitrocellulose, aka guncotton.

The first thing to realize is that cotton can be nitrated to many different degrees, ranging from slightly faster burning to explosively fast.  It’s also very difficult and expensive to wash out all the acid from cotton during manufacturing.  This didn’t always happen.

Guncotton’s potential for explosives was quickly recognized and a significant effort was made to find a way to make it moldable.  The next major step arrived with Alexander Parker who found he could dissolve nitrocellulose in molten camphor in 1854.  

The resulting material could be molded when hot and cooled to a material resembling horn.  Parker called it Parkesine  (darn clever of him!) and patented it.

Unknown to Parker, an American was developing billiard balls (ivory has always been expensive and hard to work with) from this material.  He was John Welsy Hyatt and he got his American patent in 1870.  Hyatt patented the process and not the material.

Celluloid soon became the polyester of its age and Hyatt won the Perkin Gold Metal in 1914.

The first problem was flammability which can be reduced by adding fillers and pigments.  Many of these pigments created problems later.  The second was nobody gave a thought to the life span of celluloid.

Camphor acted as a plastizer for the nitrocellulose.  These two chemicals mix to form a mixture like rice and beans.  And like rice and beans, the mixture can be uneven and you can separate the components.  When this happens to chemical mixtures, the overall property of the bulk material changes.

Camphor sublimes, changing from a solid to a gas at room temperature.  Depending on the temperature and other factors, like manufacturing stresses and the recrystalization of nitrocellulose, the camphor will sublime at different rates.  This loss of plastizer makes the remaining celluloid brittle and fragile.

If this isn’t enough, nitrocellulose complicates the issue.  Any acid remaining helps the nitrate groups pop off the cellulose molecule.  This free acid catalyzes the reaction increasing the rate of damage.  The acid vapors also defuse out of the celluloid and can attack surrounding metal, nearby metal objects and other celluloid objects.

The free acids react with fillers and colorants which change volume, liberate different acid gases, create heat and more stress and free water.  Moisture adds to the problem as the water helps form more acids and is available for other reactions.

As I mentioned before, you can nitrate cellulose to different degrees, which affect the quality of the original celluloid.  But why use nice clean cotton when you can use cheap wood chips?  Wood chips contain a molecule called ligin, but cotton does not.  Ligin can be slowly decomposed by ultraviolet light present in natural and artificial light.  The breakdown products are various organic acids which add to the mess we and our collectible knife are in.  So initial quality counts!

Lastly but perhaps most importantly, heat affects chemical reaction rates.  One study I read indicated that two months of hot summer storage in an attic at 140 F will cause as much damage as 160 years at 68 degrees.

So what does it mean to the knife collector?

Basically, you’re screwed.

If your celluloid-handled knife looks great, it will remain that way until it starts to decompose.  Once it starts the damage will accelerate.  Any plans to preserve that knife for grandchildren, or for the knife to appreciate in value will require expensive options.

Unless you’re a funded museum or wealthy, you might be better to stuff the money into your mattress.  If you truly do have a rare and museum quality celluloid-handled knife, that might be a different story.  Just remember, you can never get ahead in this game and you can only stay even for a short time.

Still want to preserve it?  Here are the recommendations from the professionals

• Stop handling it!
• Store it in dry air, 20-30% relative humidity.
• Chill!  Store at 2-5 degrees F.
• Don’t look at it.  Store behind Plexiglas UF3.  Maximum permissible illumination - 50 lux visible light, and no more than 75 microwatt of UV.
• Let it breath.  Exchange the air in the storage container with filtered and conditioned air (temperature, oxygen, humidity, ozone, etc,) in sufficient volume to remove all gaseous decomposition products that form.
• Be aloof!  Use cases and surfaces which are acid resistant and don’t corrode.  Do not store with other nitrocellulose products, textiles, metals or other objects what can be affected by acid.  It is suggested you use an activated carbon cloth and change as required.  Of course this means monitoring.  For everything imaginable.  There are chemical and electronic sensors that measure O₂, O₃, temperature, moisture, acid vapor, organic and inorganic as well as quantifying nitrogen oxides, which are a measure of breakdown rates.

Are we done yet?

Almost!

No curator would ever try this.  The curator union would break his fingers, but knife collectors get ideas.  Never wash a celluloid handled knife in water.   I know you.  You’re thinking a little household ammonia water and it'll neutralize the acids.  Don’t do it!

Old deteriorated celluloid can be water soluble and your handle could fall apart.  And more importantly, bases, like ammonia also catalyzes the breakdown of nitrocellulose.

In short, you can’t win this game.  Celluloid was unstable from the second it was made and it continues to degrade.  The best you can do is to delay the final outcome.  But there is some good news.  We’re talking about museum archival lifetimes.  This can be longer than a human life span.

 If your knife is in good shape, it could last you for years with reasonable care.  Its original quality and the care it’s received can make a big difference.  Follow the above recommendations as best as you can with a reasonable effort.  Don’t do stupid things like, rinse it in gasoline or leave it in a glove compartment in a parked car in Arizona for two weeks during the summer. 

My prescription, if I could write script, would be to enjoy the knife to its fullest while you have it and the future be damned!