Hi Nigel,
Perspex is notoriously prone to getting scratched and marked. A while ago I revamped some perspex display cases which had big scratches on them. What I did there was to go over the scratches with some fine sandpaper (which initially and shockingly made these parts of the cabinets completely opaque...). I then used successively finer polishing powders to polish the perspex clear again. The result was pretty good, but it took a couple of days of very hard and patient work.
If the perspex blocks are only marked but scratched you could try a super fine or ultra fine (800 - 2000 grit) sandpaper. Alternatively use a slurry mixed from lapping powders and water (we have a Logitech lapping machine for making thin sections here and therefore a ready supply of 600 grit silicon carbide powder and 1000 grit aluminium oxide powder). Lapping pastes are also commercially available (e.g. http://www.kemet.co.uk/product.asp?productID=2480&prodCat_FK=Lapping_consumables).
If using a paste or slurry get hold of a flat glass sheet (thick glass, not the window variety), add a splodge of your paste/slurry onto the glass and press the perspex block into this. Then, using moderate pressure, move the block in circles (but not always in the same direction or you might introduce some scratches yourself). If the slurry dries out add a little water from time to time. Wash under running water occasionally to check on progress. If using a coarser grade first and moving to successively finer grades wash really thoroughly (specimen and hands) between stages as not to introduce some grains of the coarser grade into the finer grade.
Best wishes and good luck
Christian
Christian Baars
Department of Geology
National Museum Wales
Cathays Park
Cardiff CF10 3NP
UK
Telephone: 0044 (0)29 2057 3352
-----Original Message-----
From: The Natural Science Collections Association discussion list [mailto:[log in to unmask]] On Behalf Of NATSCA automatic digest system
Sent: 14 April 2011 00:03
To: [log in to unmask]
Subject: NATSCA Digest - 7 Apr 2011 to 13 Apr 2011 (#2011-37)
There are 6 messages totaling 2006 lines in this issue.
Topics of the day:
1. SMELT (Osmerus eperlanus)
2. insects embedded in Perspex: how to remove damage? (5)
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Date: Wed, 13 Apr 2011 11:21:54 +0100
From: "Nigel R. Larkin" <[log in to unmask]>
Subject: insects embedded in Perspex: how to remove damage?
Dear colleagues,
An education officer at North Herts Museums asked me recently how she can clean several blocks of Perspex in which insects are embedded. There are several specimens in each block, showing their life cycle. The problem is that the surface has beome disfigured. It isn't mould or anything else that can be wiped off, it seems to be a degradation of the surface of the Perspex, making it difficult to see the specimens within. I enclose a photo of the problem. It looks like the damage needs to be polished-out. Has anyone encountered this before, or have any suggestions? All comments welcome.
With many thanks, Nigel.
Nigel R. Larkin BA MSc
http://norfolk.academia.edu/NigelLarkin
http://www.natural-history-conservation.com
Research Associate (Geology),
Norfolk Museums and Archaeology Service, Shirehall, Market Avenue, Norwich, Norfolk. NR1 3JQ.
http://www.museums.norfolk.gov.uk
Associate Member of the "Ancient Hominid Occupation of Britain Project"
http://www.nhm.ac.uk/hosted_sites/ahob/
Telephone: 07973 869613
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Date: Wed, 13 Apr 2011 11:53:53 +0100
From: Nicola Newton <[log in to unmask]>
Subject: Re: insects embedded in Perspex: how to remove damage?
Hi Nigel
Your colleague may be able to get the blocks buffed to take the surface layer of Perspex off and the specimens should be ok as they are embedded.
Cheers
Nick
Sent from my iPhone
On 13 Apr 2011, at 11:21, "Nigel R. Larkin" <[log in to unmask]> wrote:
> It
> looks like the damage needs to be polished-out. Has anyone encountered
------------------------------
Date: Wed, 13 Apr 2011 11:57:47 +0100
From: "Irwin, Tony" <[log in to unmask]>
Subject: Re: insects embedded in Perspex: how to remove damage?
I agree with Nick - polishing off the damage is the obvious thing to do, but if the resin has started to decay, it wll not be long before it has to be done again - at which point new embeddings may be a more cost-effective solution.
Tony
-----Original Message-----
From: The Natural Science Collections Association discussion list [mailto:[log in to unmask]] On Behalf Of Nigel R. Larkin
Sent: 13 April 2011 11:22
To: [log in to unmask]
Subject: insects embedded in Perspex: how to remove damage?
Dear colleagues,
An education officer at North Herts Museums asked me recently how she can clean several blocks of Perspex in which insects are embedded. There are several specimens in each block, showing their life cycle. The problem is that the surface has beome disfigured. It isn't mould or anything else that can be wiped off, it seems to be a degradation of the surface of the Perspex, making it difficult to see the specimens within. I enclose a photo of the problem.
It
looks like the damage needs to be polished-out. Has anyone encountered this before, or have any suggestions? All comments welcome.
With many thanks, Nigel.
Nigel R. Larkin BA MSc
http://norfolk.academia.edu/NigelLarkin
http://www.natural-history-conservation.com
Research Associate (Geology),
Norfolk Museums and Archaeology Service, Shirehall, Market Avenue, Norwich, Norfolk. NR1 3JQ.
http://www.museums.norfolk.gov.uk
Associate Member of the "Ancient Hominid Occupation of Britain Project"
http://www.nhm.ac.uk/hosted_sites/ahob/
Telephone: 07973 869613
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------------------------------
Date: Wed, 13 Apr 2011 12:43:54 +0100
From: David Lampard <[log in to unmask]>
Subject: Re: insects embedded in Perspex: how to remove damage?
[Message contains invalid MIME fields or encoding and could not be processed]
------------------------------
Date: Wed, 13 Apr 2011 14:15:25 +0100
From: "Nigel R. Larkin" <[log in to unmask]>
Subject: Re: insects embedded in Perspex: how to remove damage?
Many thanks to everyone who responded so quickly to the perspex query, both on- and off-list. All suggestions greatly appreciated and passed on.
With best wishes, Nigel.
Nigel R. Larkin BA MSc
http://norfolk.academia.edu/NigelLarkin
http://www.natural-history-conservation.com
Research Associate (Geology),
Norfolk Museums and Archaeology Service, Shirehall, Market Avenue, Norwich, Norfolk. NR1 3JQ.
http://www.museums.norfolk.gov.uk
Associate Member of the "Ancient Hominid Occupation of Britain Project"
http://www.nhm.ac.uk/hosted_sites/ahob/
Telephone: 07973 869613
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End of NATSCA Digest - 7 Apr 2011 to 13 Apr 2011 (#2011-37)
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