By Daniel Hubbard | July 3, 2011
I thought that since my last two posts had been about preserved landscapes and preserved buildings, I ought to make it three of a kind by writing about preserving things, something that genealogists not only can take advantage of, but can actually do. Fortuitously, last weekend I attended a program about preserving objects at the Swedish American Museum in Chicago. It was a very interesting couple of hours that filled in some gaps for me.
In a way, preserving objects reminds me of cooking. Partially because there are “recipes” to follow, though in some sense that is true of many processes. Mostly, I think it reminds me of cooking because it seems to be cooking’s mirror image.
When you cook, the food is either completely cooked or it isn’t. Almost getting food up to the temperature that makes it safe to eat isn’t a good idea. Preservation is a matter of “every little bit helps.” Everything that you do to slow down degradation counts even if far short of perfection.
The most famous bit of chemistry when it comes to preservation is what acids do to paper. The presence of acids in paper leads to a reaction that breaks the long cellulose molecules that give paper its strength. That is, of course, considered to be a bad thing. Nevertheless, when a mildly acidic marinade changes some of the long protein molecules and tenderizes a piece of meat, we generally consider that to be a good thing.
One point that came up in the discussion of acidity is that the term “acid free” is not regulated. That means that though a sleeve, folder or box to be used for the storage of papers and artifacts may be acid free now, there is no guarantee that it is chemically stable enough to remain acid free over time. To be as sure as possible of chemical stability the best bet is to buy from a reputable dealer that specializes in archival materials.
What actually got me thinking about cooking and preservation together was a warning I had not heard before. Luckily, I haven’t made the corresponding mistake either. The warning was about using buffered materials to store protein based objects. Something that is chemically buffered contains chemical components that make it difficult for the level of acidity to change. Technically, the pH is stable and usually close to neutral. Buffered paper will become acidic only very slowly if it absorbs acid. Usually this is a good thing. If a newspaper clipping is stored in contact with buffered paper it may last longer because some of the acid content of the newspaper will leech out into the buffered paper. The buffered paper neutralizes the acid and the acid can no longer contribute to the degradation of the clipping.
So why is that bad for protein based material? I had to do some checking and it turns out that the answer is the Maillard reaction, one of the most famous reactions in the chemistry of cooking. It requires both protein and carbohydrate and is what makes bread crust, toast and french fries brown. It browns meat and many other foods as well. Importantly for the cook, this reaction adds a great deal of flavor not just color.
If on the other hand you are trying to preserve something, browned and flavorful are not what you are after. Alkaline substances can speed up this reaction. A weak alkali is what puts the “buffer” into buffered paper, cardboard, etc. So the advice is not to use buffered materials when preserving protein-based materials like wool, silk and leather. Albumen prints, a type of photographic print, were made using egg white (albumen) which is rich in protein, and so they too should probably not be in contact with buffered materials.
One last bit of chemistry can be summed up with one word, “cleanliness.” Whether it is salts and oils from your hands or just dust, it probably isn’t good for what you are trying to preserve. Every material is different and every source of grime is different so it is hard to give hard and fast rules. Trying to clean something might be a good idea if done right and right always includes doing it carefully. Other times just keeping things as they are and keeping new dirt away is better than anything you try to do to clean.
Energy in the form of heat, sometimes even in the direct flame, or perhaps microwaves (which are converted to heat in the food) is strictly speaking what makes cooking food different from just preparing it. Adding energy causes some chemical reactions that would happen anyway to happen faster and allows other reactions to take place that would not occur without that heat.
Energy might be necessary for cooking but it is bad for preservation. Obviously, you don’t want to heat things that you want to preserve but there are other forms of energy that are more ubiquitous than oven-like temperatures. Visible light and UV pack even more energy, particle-for-particle, than heat. Both are famous for causing fading of photographs, inks and dyes. UV delivers more energy than visible light (easy to remember if you know that UV is the part of sunlight that causes sunburn and that visible light doesn’t) and since we don’t see UV, museums filter it out of their lights. Because even visible light causes problems, sensitive objects should not be exposed to more light than necessary. Even though scanning and photographing involve light, the benefits of having digital images to inspect so that you do not need to take out the object itself, generally gives less light exposure over time. So digitizing is a great way to reduce long term light exposure. Having digital copies (notice the plural; make backups!) also helps to ensure that details that fade from the original are still available for checking and, if worse comes to worse, that something remains if the object is destroyed. It is ironic that preserving things in the best possible way often means storing them so that they can’t be seen.
Often in cooking, you want to do something to the food suddenly. Heat popcorn very slowly and you will end up with something a lot like ball bearings. Heat the kernels quickly and instead of the moisture slowly leaking out, it will explode the kernel and you get a tasty snack. Sear the right piece of meat and you lock in the juices and add a lot of flavor to the outside. Heat it much more slowly and you get something that you won’t want to eat at all.
Shocks may often be good when cooking but they are bad for preservation. Ideally conditions like temperature and humidity should be the same as what makes people comfortable. They should also be stable. When they aren’t, they should change slowly. You can think about it this way. Changes to the environment affect the outside of an object first and then spread slowly toward the interior. If the change in the environment is rapid, the exterior of the object might shrink or swell much faster than the inside. The results are not pleasant as anyone who has driven a road that has been through too many freeze-thaw cycles can attest. Your old objects might not develop potholes like a road does but they will slowly become worse for wear.
One bit of advice from the presentation on this topic is that when you can’t provide a stable environment for what you are trying to preserve, put it in layers of protection. After all, if the problem with an unstable environment is that the outside of the object feels the affects rapidly and only slowly passes them along to the interior, then giving the change in the environment lots of layers to slowly propagate through has the effect of slowing down or even preventing the change from reaching the object. It is the same idea as what happens deep down inside a cave. At the surface, it might be summer or winter, night or day but the temperature in the cave is stable and will be roughly the average surface temperature.
The repeated folding that kneading entails, causes changes that give bread dough the strength to hold together and rise. Great for bread dough but the strain of folds is bad for paper and cloth. Folds and creases are to be avoided. Paper should be stored flat even if once folded. The damage that takes place at folds occurs over time not just the instant that the paper is folded. Flattening helps. Cloth behaves similarly and cloth articles that are too large to be stored flat should be rolled or gently folded (and periodically refolded to avoid putting the strain all in the same part of the fabric for too long. We were shown a one hundred year old wedding dress that was stored using “sausages” of acid-free tissue paper to gently curve the cloth into waves so that no part of it was folded.
A Watched Pot
One place where cooking and preservation are similar is in observation. In cooking you keep an eye on things to make sure they are progressing correctly. In preservation you keep an eye on things to make sure nothing at all is progressing. The same activity but with different rationale and on a different timescale. At first you might think that once you have packed something away, you would only take it out to investigate it or to show someone your treasure. It turns out to be wise to examine them every so often as part of preserving them. The point is that if something starts to happen, you want to know about it. If humidity gets trapped and starts to cause mildew, you want to catch it early. If mice or insects get into your packaging you want to know. You don’t need to be paranoid but check on occasion is wise. Another tip was that it is better to check at different times of year to avoid always checking when the conditions just happen to be perfect.