Egyptian artifacts

[kpf5097]

Hi,

I'm a young preparator assisting in the organization of an exhibit of Egyptian artifacts. Our last registrar, who is gone now, had placed 2 or 3 terra cotta bowls in a micro-environment with dessicants. Can someone explain the purpose of this to me? I understand the need to keep the moisture/humidity low, but I'm also concerned that a humidity level that is too low may cause unnecessary drying and cracking to the pottery.

Secondly, we are placing this exhibit in a space flooded with natural light. I know that stone, metal and terra cotta objects themselves are not in much danger from the uv light, but I was slightly concerned about the unglazed pigments on some of the pieces. We also have a relief fragment from the wall of a temple. Any thoughts on possible uv damage to these pigments?

Thanks

[JasonO]

I'm not a good person to answer this question (which is more about conservation), but I would post it to the PACCIN listserv pacinlist@listserve.com (you'll get a faster response) and try signing up for the RCAAM listserv, (http://0338c93.netsolhost.com/Listserv) they are pretty fast. Jason

[kpf5097]

Thanks Jason,
no replies yet...

[T. Ashley McGrew]

Hi,

The use of a true micro climate is relatively unusual to find used for ceramics which are not hygroscopic in nature by themselves. The only reason I can think of that it might be called for is if they are "salty pots". This is when a pot has either been buried in an environment that contains minerals that leach into the pot overtime or pots made with a clay body that already contains a high level of natural salts. In either instance if the humidity gets high enough (I want to say around 65% but I can't remember) the salt crystals become active and the surfaces may start to spall. The ceramic may start to destroy itself essentially from the inside out. I have never heard of there being a concern about ceramics getting too dry though.
If there were a reason for concern it could be about a reaction of a glue used in the past for conservation purposes. One of the nasty surprises you can encounter is an object that has been repaired and the fill so well in-painted that it is essentially invisable. An object like this may appear to be solid but will only be as sound as the glue that is used. In many old objects there may not be accurate records about what glues were used, how well they were prepared or even that treatment ever occurred! So in that case the glues themselve could theoretically react to humidity changes over time causing the joins to weaken....

I am sure there could be exceptions, but I personally am unaware of concerns about UV exposure related to normal display of pigments on stone.

[kpf5097]

Thanks for your help!

The objects are very old, around the first dynasty. I'm sure they were burried in the sand for thousands of years, so the salt could be possible. I could be wrong, but they dont appear to have been repaired or glued at any point. And our museum is completely climate controlled, the humidity in the vault never goes much higher than 50.

[kpf5097]

And actually... if I remember correctly, there is some spalling on the pots.

Perhaps I should place dessicants under the vitrine with it when we set up the exhibit? It will likely be up for 4 or 5 months.

[T. Ashley McGrew]

Just out of curiousity what relative humidity is your silica gel conditioned to anyway?

[kpf5097]

Good question. I have no idea. Our last registrar put a date on the box of when she placed the objects in the micro climate. I need to check how long ago it was, I probably need to replace the dessicants. Its probably been several years.

[T. Ashley McGrew]

Hi,
Typically any kind of dessicant will cease to be effective over time. Most of it has to do with how well the case is sealed. a pin holes worth of gap in a gasket can cause its effect to decline rapidly. Decline would normall start long before a year. If the material inside really requires it. You will want to change it out and place a miniature thermohygrometer in the case (usually in a back corner) where the conditions inside can be monitored. I am putting a link to one that I have seen used alot but you might want to ask around as I haven't purchased any in a while.

http://www.apsnyc.com/index.php?page=humidity-measurement

[kpf5097]

Yes, I knew that the dessicant would become ineffective over time. I guess I'm just curious as to how delicate a piece spalling pottery actually is. The vault is already temp and humidity controlled. I don't think it gets any higher that 50% rh.

[T. Ashley McGrew]

In some cases they can literally crumble just sitting on the shelf. First indication may be slight irregularities to the surface that develop into bulges. Those bulges can eventually just fall off leaving a pile of "powder" at the pots base. Once it is visibly bulging it may take only the slightest contact to result in pile of powder left in your hands that loosely matches a concave void left in the side of the vessel. The main thing is though that if you have a stable controlled environment hopefully the condition is not really "active".

[kpf5097]

Thanks for all your help!