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David McKay 21-07-03 02:46 AM

cleaning an egg tempera surface
I have asked this question in the past and have received different answers. Now with a conservator looking in I would like to ask again. Lorraine: How would you recommend cleaning an egg tempera. I am talking about one that is well cured, (a few years old at least), and would like to just remove the regular dust oil etc that would have accumulated from the air. I have used a soft cloth saturated with turpentine and have gone over the painting quickly and lightly as it is laying on a table horizontally. Then I lightly went over it again with a soft dry cloth to pick up some of the turpentine then just left it to dry on its own. I seemed to get a brownish colour on the cloth with no obvious pigment colour, and I saw no change in the painting as might be the case if some pigment was dissolved. Is this a good practice?? What about alcohol for cleaning?? Which would be more effective, safer etc.?? My medium is pure egg yolk and water, no oils or preservatives.


21-07-03 03:39 AM

Dear David,

My answer depends on a number of conditions. I am assuming you've not added any kind of surface coating to your painting such as damar or a synthetic resin. Also, I'm assuming that you do not have any water or oil gilding on your painting.

To prevent having to clean the surface of your paintings, I would like to say that I recommend you frame your egg tempera paintings behind glass with a suitable spacer between the glass and the painting. That's the ideal situation to avoid having to clean the surface.

I don't recommend using turpentine or alcohol to clean the surface grime from your painting. Turpentine is a surprisingly harsh solvent--the fact that you're picking up some brown substance doesn't mean you're getting up dirt alone--surface grime is usually grey in color. You could be leaching oil from the surface. I'm really glad you don't seem to be picking up any color, however--that's very positive.

I don't recommend trying any alcohols. Alcohols literally rip the oil molecules from the surface of a painting. We use methanol or ethanol mixtures to remove tough oil overpaint or oil varnishes on paintings--and these mixtures are one of the last resorts available because of the strength of the solvents. There's not a lot of oil in egg tempera compared to linseed oil paint, so you kinda want to keep everything you've got there. :)

I have to say that rolling over the surface with a cotton swab dipped in a good quality odorless mineral spirits would likely be fine. Have a fan nearby to help evaporate the solvent and wear a respirator. Just because it's odorless doesn't mean it's harmless. Stay away completely from any areas of oil gilding with your solvent. Don't soak the surface with the solvent and be sure to *roll* the swab, not scrub. I would not rub the surface with anything else as there can be some abrasion damage done without you even noticing. That's what I would do with a relatively young oil painting, but be sure to test the colors first.

You can also try rolling over the surface with a very dry swab in distilled water--BUT--only if you have *no* water gilding and your support is wood instead of cardboard. And do not use water if you have *any* cracking of any kind. You could easily undermine your gessoed surface and cause lifting and flaking. Look for those things, be extremely careful, and especially do not soak the surface.

Stay away from things like detergents--people think Ivory is a mild soap--and in terms of pH it is mild--however, the sodium lauryl sulphate in the soap needs to be rinsed more times than most paint surfaces can stand safely. The detergent, if not rinsed completely away, can chemically combine with the paint. In an extreme example, a painting had almost been literally bathed in the substance and the sodium lauryl sulfate was completely embedded in the paint. Within a short period of time it began to migrate to the surface of the painting, creating a hazy grey film overall.

The less you do the better. It has been scientifically verified by numerous researchers that *every* time you clean a painting, either with organic solvents or water based aqueous systems, you still remove paint at a microscopic level. The damage being caused may not be evident immediately to the naked eye. It's like light damage--it's cumulative.

A painting framed *properly* behind glass, kept in a stable environment, is the cheapest and best preventative conservation you can get. Those that object aesthetically to glass can find a type of glass with a refractive index that is close to that of air. It's an amazing thing, though kind of expensive. I think it's called Museum glass or something like that. I saw a number of Impressionist paintings covered with this in a show recently. I couldn't see the glass until I was almost nose to nose with the painting. Very impressive stuff.

I hope that answered your question and I sure hope I've been a help. Geeze, I've written a novel--my apologies. Take care!

David McKay 21-07-03 03:59 AM

Thanks so much Lorraine, I really appreciate your time and thoroughness to this topic. I am not sure what you mean by "rolling" the cotton swab. Are you using something larger than I am thinking of, that is of a swab about an inch or so wide? Also, are you suggesting that mineral spirits is less harsh than turpentine?

I have never liked the idea of framing my temperas under glass but if there is a product that is as invisable as the one that you mentioned, maybe I should look into it, no pun intended. I have heard of a glass called "den glass", maybe that is it.

Anyway thanks again. You have been very helpful.


hisstah 21-07-03 04:54 AM

Dear David,

After looking at my earlier response, I can see that rolling with a swab must have sounded rather weird. :oops: The cotton swab I was referring to is a cotton Q-tip used to clean your ears. You can make your own by getting real cotton like people use to remove makeup and rolling it onto small bamboo skewers. But it might be easier and faster to buy a package of the Q-tips. Once you practice a bit with rolling the Q-tip on the surface, you can get an idea of how much pressure you can safely use. Be sure to change your swabs when they become grimy. Don't want to smear the dirt all over. :)

I'll double check on the chemical compositions of both mineral spirits and turpentine, but I know they're both basically hydrocarbons. The turp derives from the gum of a pine tree and the mineral spirits is a petroleum distillate. I think my prejudice against turpentine comes from the fact that it is often impure with oleo-resinous inclusions that can be transferred to the paint surface. Also, if I'm remembering correctly--and it's *always* possible that I'm not--sometimes there are other impurities in the turpentine such as aromatic solvents which are stronger than straight chain alaphatics like mineral spirits. Again, I could easily be wrong and I'll check on that and get back with you.

Highly refined turpentine is probably just fine--again, it's likely my personal prejudice making me say things that are not completely accurate. Chemistry classes were awhile ago and I'm a bit rusty. :oops: Sorry about that.

You are not alone in your dislike of using glass on paintings. I dislike it also. But if I could afford that non-reflective stuff, I'd use it all the time. :) From a conservation standpoint, I highly recommend covering paintings with glass. I think you may be correct about the name "den" glass--that sounds familiar. Your local framer will probably know. Just don't let them tell you non-glare glass is what you're looking for. I'm pretty sure that's not it. Take care and good luck! Hope I haven't muddled things up too much.


David McKay 21-07-03 02:11 PM

Dear Lorraine:

I know that regular non glare glass looks foggy as soon as the artwork is set back from it. I believe the Den Glass that I have seen advertised, is non reflective as well as having the ability to block out almost all of the ultra violet rays of the sun. I don't know if it will display the same "foggy" character as the less expensive stuff.

There was a question from Meg awhile ago, asking about mould on her husband's painting. I gave an answer but if you had the time maybe you could look at that conversation and add something to it??? How long would you leave a new tempera work to cure before framing behind glass?

Thanks again,


hisstah 22-07-03 12:01 AM

Hi David,

To be honest, I don't think you need to wait long at all before framing an egg tempera painting behind glass. The initial drying takes place by evaporation of the water and the oil then dries " the slow hardening of the oil which remains suspended in the albuminous matrix. This oil content is greater than that of the albumen and, in consequence, the ultimate film is very little affected by water." (Painting Materials-A Short Encyclopaedia by Gettens and Stout, page 21). Emulsions are funny things, but I suspect the oil dries in a similar way to linseed oil, which means that it oxidizes and possibly eventually cross-links. I will double check that, but regardless, that way of drying will not be impeded by framing behind glass. As long as the water has evaporated, it shouldn't affect it at all.

I've got a little bit more info on turpentine, odorless thinner and mineral spirits. Turpentine is a mixture of various turpenes--which are aromatic hydrocarbons--distilled from oleoresinous gums or balsam of pine. Aromatics are defined as solvents based on the benzene ring. I've tried to find a diagram of the turpenes molecule to see how it is constructed or if indeed there are any benzene rings, but no luck so far. (I have to say chemistry was not my strongest subject in grad school--my apologies. Anyone else out there who knows this stuff please feel free to chime in at any time.) But xylene and toluene are extremely strong solvents and both are aromatics.

Odorless thinner is an aliphatic solvent with no aromatic content. (Mineral spirits is also an aliphatic but it does have *some* aromatic content.) Alipahtic solvents are usually innocuous to most aged natural resin films and to aged oil films.

I was taught that, in general, aromatic solvents are much stronger solvents than aliphatics. Which is why I had in my mind that turpentine was stronger than odorless thinner and shouldn't be used on newer paint films. And when I say newer paint films, I mean under 20 years.

I'm glad you asked these questions--I needed to knock some of these cobwebs loose from my brain. Thanks and I hope this has been a help. If I find out anything else or find out that I've given you any incorrect information, I'll be sure to let you know. I'll go check out the mold question next.


hisstah 22-07-03 12:33 AM

Hi again, David,

Just found a diagram of the main constituent of turpentine, which is called alpha-Pinene. Wish I could post it here, but I'm not sure how. The molecular shape is indeed a benzene ring. It's very similar in shape to xylene with a few more methyl groups, but two fewer double bonds. Xylene is often too strong a solvent to use on fairly new paintings.

So it seems to indicate, from what I recall from chemistry class and from using them in my work, that aromatics are stronger than most aliphatics, especially alipahtics with no aromatic inclusions. Hope that made sense. So I'd say it's a fairly safe bet to use odorless thinner as opposed to turpentine.


jason_maranto 26-07-03 01:14 PM

Museum Glass is made by Tru Vue and is amazing stuff ... I've used it for several pieces in my gallery as well as for some customers on special pieces.

It can be pricey but it is worth the money for original works of art in my opinion -- (not everybody has the same pricing stucture as I do) however my prices are pretty reasonable for small frames (under 16 x 20)

Framers will pay roughly $120 for a 32" x 40" sheet of museum glass at thier cost -- so that knowledge should give you some leverage at the design counter.


David McKay 02-08-03 02:52 PM

Hi Jason:

Thanks for the info regarding TRu Vue Museum Glass. I have visited their website in the past and I use their products for my watercolour paintings, although I have never used the museum glass. I am not clear of the process they use to cut down on the reflections in the museum glass. They mention etching one side of their "reflection control " glass. Do you know if that is also the case with the museum glass? If so, do you loose some clarity if the glass is positioned a distance from the work? I would probably try putting the glass between an outer wood frame and a linen liner, which would hold the egg tempera painting, so that the glass and painting would be about 1/4 inch apart.

Thanks, David

jason_maranto 02-08-03 11:04 PM

"reflection control" is just a fancy term for non-glare glass -- which will have a fuzzy appearance to some degree.

Museum Glass is virtually invisible(crystal clear) from any depth... they achieve the anti-reflective qualities of the glass thru a (I believe) quartz based micro-coating which distorts the light waves enough to allow nearly complete light penetration thru the lite of glass (1% of light is absorbed by the glass). This is important because things look brighter behind Museum Glass because regular and non-glare glass each reflect roughly 7% of the light back at the viewer.

The only dissadvantage (besides price) to Museum Glass is the fact that the coating can be scratched and does tend to pick up fingerprints rather easily... wearing cotton gloves when handleing it would be advisable.

Other features of Museum Glass:

97% UV filtering to protect from fading.
low iron glass so the green tinge in ordinary glass isn't present.
Cuts easily using standard glass cutter (this is more important than it seems, many competitive products require special cutting and cleaning proceedures)


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