How to remove scratches on a fresnel?

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#4
I also have a fresnel problem - I took the plastic fesnel (thick plastic not a page magnifier) out of my OHP and cleaned it with a "screen cleaner" wipe - the kind used for monitors on work computers.
The problem is that the fresnel developed a white substance on its surface. If you gently scratch at it, it does come off a bit, if you wash it in water it goes, but then comes back again when the thing dries.

I've tried cleaning it off with window cleaner, vinegar and meths, but all seem to clear the white substance off until it dries, then it comes back. Very strange - Does any one know what it is/how to get rid of it?

The only good part of it is that although I can't see through the fresnel when looking at it (due to the white substance) I am still able to project through it. I want to get rid of it though as i'm sure the image would be better without it.

Any ideas on how to fix it - or how I went wrong would be appreciated.

JT
 
#6
The wipe probably had a Windex type of cleaner on it. That's fine for glass, but not acrylics and plastics. Anything like Windex, or ammonia will wreck them, that's why they have special cleaners for plastic such as Novus plastic polish.
 
#7
The fesnel doesn't have an obvious rough side - it's all enclosed inside plastic, it effectively looks like a sheet of perspex (plexiglass?) with watermark inside. The white stuff is more a residue than flaking, almost like it has talcum powder solidified on the outside.

I think it must have been the first screen wipe, as wylie-c said, that reacted with the material. ******.

ah well, at least it still works.

Thanks guys.
 
#8
Hi, I'm only a Newbe, but i think that your problem with the whitening on your lens is that when you wiped it first of all, you took off the polished surface from the lens.
If, as you said in your last post, the lens is flat, with no ridges like a thin fresnell , you could try to polish the surface back to a shine.
I would'nt use an electric buffer, as just to much speed, or holding in the one place for too long, will surface-melt the lens, fecking it up for projecting, alltogether.
Hand polishing is an option, although, i'm not sure if this will give an even finish.
I have had success polishing turntable lids that were scratched and abrased, using a car polisher type buffer in an electric dirll, it has a large area, so does'nt heat up as much if stationary for too long.
I think that it is made of wool, being white and furry, but not sure.
I would try to get the same reaction on an other bit of plastic, and try polishing that first.
Hope this is of some help,
D2D
 
#9
Hi again, just another mad idea for partially mending white stuff on lens problem.
You could try using a stanley knife blade to gently scrape away the white, although this would take a lot of patence, but if you drag the blade, sans handle, backwards, it should help.
I had the same problem when i was 14, i spilt nail polish remover, (not mine), the acetone in it reacted with the plastic surface on a hifi systems lid, (my Dads).
I tried every type of polish in the cupboard, no success, i had'nt realised at first that it was on the hifi, so it got the chance to sink well in, left two shallow pits, about 1 inch round.
I finally settled on brown boot polish to disguise the damage as my da was due home anytime.
Having spent a sleepless night, thinking how to solve my dilemma, I thought of the stanley blade method.
Next time he went out, i put it to the test, semi success! as i was using an old, rusty blade, but improved it, nonetheless.
If contemplating this method of last resort, use a new blade, and scrape towards yourself, keeping blade at 45 deg with edge away from you, doe's this make sense?
I'm sure that you know what i mean.
after scraping, you could then use a large buffer to smooth any accidental scratches.
Use at own risk!!
could'nt hurt to try a small corner.
🙂
D2D
 
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