Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Raising pH of coffee/tea safely and permanently?

  1. Mar 5, 2017 #1
    I don't know much about chemistry but was hoping that some of you guys could help me with a quick question. I build wooden model ships of sail as a hobby. One "trick" for giving sails and rope an aged look is to dip them in coffee or tea and let the tannin dye the materials. The problem is that these liquids are (of course) acidic. Some folks say this is a bad practice because, over time, the acid will cause the rope and sails to break down. Here's my question(s):
    Is there a safe and easy way to neutralize the coffee/tea?
    Will it be permanent? The reason I ask this is because in adjusting the pH in my aquarium hobbies, I have found the effect to not be permanent.
    Is there an easy way to calculate the resulting pH before making any adjustment?

    Thanks in advance for any help!
  2. jcsd
  3. Mar 5, 2017 #2

    jim mcnamara

    User Avatar

    Staff: Mentor

    One way: Buy low acid coffee Hevla Coffee®, Simply Smooth®, Gentle Java® or Puroast®. These increase pH slightly. Regular coffee ranges in pH from 4.2 - 4.8 or so. (personal observation). It is a natural product, subject to all kinds of processing and mixing of varieties, so it is not going to be a constant. Store brand instant coffee varies from time to time.

    You can buy test tabs that you dunk into liquid - which show pH. Addition of mild bases like a few drops of dilute lye will raise the pH. Lye is NASTY. Be careful.

    Plus, IMO, the pH you have for tea or coffee is above the point where you find degradation of plant fibers, e.g., high acid paper in old books.

    Here is a slightly technical article about conservation of acid paper. Note the pH levels are really low.
  4. Mar 5, 2017 #3


    User Avatar

    Staff: Mentor

    I am with jim on the "pH not low enough to be a serious problem" idea.

    Any base you add (lye, caustic soda) will raise pH. Amount to use has to be determined experimentally, no way around it. However, changing pH can change the hue of your "paint".
  5. Mar 5, 2017 #4
    Couple of very interesting notes. Awesome responses! I had not even entertained the notion that the hue may change with the pH. Perhaps the pH shouldn't be a consideration after all. I'm getting more convinced that the comments regarding long-term degradation may be more a product of speculation than a true concern. But what would one expect from a bunch of guys who spend their time constructing 17th century replicas? :)
  6. Mar 5, 2017 #5

    jim mcnamara

    User Avatar

    Staff: Mentor

    Aside from clod like children, your models biggest enemies are:

    Secondhand smoke - permeates everything, adds smell and a yellow color

    UV light - Wood sunburns in direct sunlight - dark timber species become pale, light species become darkened. Even inside this occurs. Cherry furniture is notorious for darkening over time. UV also destroys lignin, mostly in direct exposure which causes film finishes to lift and crack, unfinished or raw wood to fuzz up. Classic fuzz example: teak bench been outside for several years, note the hard little fuzzies on the exposed surfaces.


    In some places, the smog component PAN can damage things like polymers and rubber.
  7. Mar 5, 2017 #6
    All very good to know! And the even better news is:

    No smoking
    The room in which I display my ships is pretty free of direct sunlight (only in the evening hours).
    I live in a place where the prevailing winds blow toward the nearest city - 35 miles away!
  8. Mar 5, 2017 #7


    User Avatar
    Gold Member

    The air that you bubble through the water has CO2 in it. This acidifies the water. The fish and other organisms that call the aquarium home also alter the PH.

    Another method for keeping you models in good shape is to keep the humidity at a constant fairly low value (not too low as that presents other problems). If you can keep them in a display case the museum folks should be of help.

  9. Mar 5, 2017 #8


    User Avatar
    Science Advisor
    Gold Member

    Conservation technicians working with paper documents and art work have developed safe methods for neutralising acidity .

    This was quite interesting
  10. Mar 5, 2017 #9
    Yes. I had forgotten about the factors you mentioned regarding the aquariums. I did learn another helpful trick regarding coffee; apparently, cold brewed coffee is significantly less acidic than the more common hot brewed. According to one source, hot water releases the acid within the bean and that's why hot brewed coffee is more bitter.
  11. Mar 5, 2017 #10
    Yes, very interesting. Apparently, I should shoot for slightly alkaline to account for the CO2 in the air - if I want it to last hundreds of years! :)
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted