Soft pastel or oil pastel?

[Not your average framer]

Other than basic visual inspection and the old fashioned "rule of thumb" stuff like the cotton bud test, does anyone know if there is a more scientific and definative test to confirm if a pastel drawing is soft pastel or oil pastel?

I'm almost certain that two old pastel drawings in for cleaning are oil pastels, but I would like to be sure as the cleaning process is completely different for the two different types.

The guy who trained me in bookbinding and paper conservation always knew the answers to things like this, but he never taught me this one and unfortunately he died before last Christmas so I can't ask him.

[prospero]

The last oil pastel I saw was yonks ago and I seem to remember it had the look of wax crayon. Of course it would depend on the way it was applied. The one I remember was done on velvet.
Can't remember if it smelt oily either, although maybe if they do smell it might go off after a few years.

That's the sum total of my knowledge of oil pastel.

[Not your average framer]

The sum total of my knowledge doesn't go much futher than that either. The following are the tests and visual inspection methods I intend to employ. I don't say that they are right, they are just the best I can think of.

1. OIl pastels stick to the paper much better and tend not to lift off onto low tack adhesive tape. Where as some soft pastel pigment material would be expected to adhere to the low tack adhesive tape

2. OIl pastels tend to faily shiney which viewed under illumination and optical magnification, where as soft pastels are less so. I've seen this for my self, but have not had this independantly confirmed. I think I need to buy some soft and oil pastel sticks so I can compare for accuracy.

3. Gentle rolling with a dry cotton bud should not pick up any pigment from an oil pastel. The binders in oil pastels should keep the applied pastel material together in one mass where it has been applied as one mass. Therefore it should not result in shedding of loose pigment to anything like the same degree as soft pastels.

4. Careful use of an alcohol soaked should after a while start to pick up a small amount of pigment. Ideally this should be done on an area of pigment where the is little risk of spreading any pigment onto bare paper of an area of a different colour.

5. Oil pastels often are applied with more body and where applied may show so degree of raised impasto.

[Not your average framer]

I can now report that I have carried out most of my intended tests prior to cleaning and have concluded the they are both oil pastels. I did not do the alcohol test or adhesive tape test, (I have some very low tack fully removable tape). However, having had time to think about it, I wasn't so sure about these ideas so I decided not to do these at all.

Both have now been soaked in the usual 2% chlormine T solution, but still could do with a second go in another batch of the solution as they are both very heavily foxed and a few spots look like they need some more.

I don't know I would recommend my previously mentioned tests on just the basis of two pastel drawings, but they are certainly something to give some thought too, if anyone else is in the same situation.

I have ammended my list of tests, which now are:

1. OIl pastels stick to the paper much better and gentle rolling with a dry cotton bud should not pick up any pigment from an oil pastel. The binders in oil pastels should keep the applied pastel material together in one mass where it has been applied as one mass. Therefore it should not result in shedding of loose pigment to anything like the same degree as soft pastels.

2. OIl pastels tend to faily shiney which viewed under illumination and optical magnification, where as soft pastels are less so. I've seen this for my self, but have not had this independantly confirmed. Your own small stock of soft and oil pastel sticks would be helpful so you can compare for accuracy.

3. Oil pastels often are applied with more body and where applied may show some degree of raised impasto, which could be an extra visible indication.

I think that the on site availability of pastel sticks of both oil and soft pastels are advisable so that your can compare known samples of each as a means of reference.

Any negative indications would indicate a need for futher verification before proceeding. The balance of probabilities is not proof and certainty is a responsible requirement when cleaning a customers property!

This information has been added for those on this forum who already know what they are doing and may find this useful. It is not encouragement for others without adequate training and experience to attempt the same thing. I was trained how to do this and even then I often need exercise considerable caution.