Fixing a rusty iris diaphragm on a Baker Series IV microscope
I recently bought a Baker Series IV, I wasn’t planning on buying one but my friend, Merv, convinced me that I should. I don’t take a great deal of convincing because I’m a sucker for any microscope. I think the persuasion went something like this.
Merv said:
“There’s a Baker Series IV for sale, they’re nice microscopes.”
– I bought it.
It was cheap but it’s not in a great state. It has rust patches and bubbles in the paintwork. Bits that should move freely are stiff and bits that shouldn’t move at all wiggle. The usual second-hand microscope problems.
This time though there was a more serious problem. the iris aperture was rusted, badly rusted; it’s also a fiddly horrible design, the edges of the iris blades are bent up and the whole thing is quite fragile. I don’t like taking iris diaphragms apart at the best of times and I definitely didn’t want to take this one apart so I did what any sensible human being would do. I called my friend and asked him how to fix it.
“It’s simple” he said (he says that a lot) “isopropanol, de-ruster, isopropanol, WD40 and a soft toothbrush”
Guess what? he was right, it was simple, so I thought I’d post it here, in case anyone else finds it useful.
STEP 1 – Observe the horrible rustiness of my aperture iris. I attempted to remove the iris diaphragm carrier from the microscope but I failed because I couldn’t turn the screw I needed to turn. I have hypermobile joints and a rubbish grip, my husband was at work so I couldn’t get him to do it. I had to work with it in situ. I popped some absorbent cloths underneath the carrier to protect the field iris/condenser lens beneath and continued.
STEP 2 – cover the rusty iris with isopropanol and give it a gentle scrub. I didn’t have a small enough toothbrush so I used a foam camera sensor cleaning widget. I prefer them to cotton buds because they don’t leave fluff behind. They’re more expensive than cotton buds but I use them quite a lot in delicate areas. Quite a lot of surface rust has come off already, see?
STEP 3 – after the isopropanol has evaporated cover the iris in de-ruster. I use Renaissance Metal De-Corroder.
The Renaissance blurb says:
Treatment selectively ruptures the bond between base metal and corrosion layer, reducing rust to a sludge which is easily wiped or brushed away. Clean-water rinse stops the process.
Even relatively prolonged immersion over several days has no significant effect on sound metal, thus giving the conservator complete control over the process – and freedom from it.
The totally benign nature of the product eliminates work and health hazards associated with common de-rusting systems such as those based on phosphoric and hydrochloric acids.
I can’t fault it, but it is expensive, so use an alternative if you wish to. In the next picture you can see the Renaissance De-corroder doing its thing. I put it on with another foam camera sensor cleaning tip and left it to work for an hour or so. I gave it a gentle scrub every now and then. It’s all very scientific.
Step 4 – Rinse off the metal de-corroder with water, allow to dry (use isopropanol to help it on its way if necessary) then give the iris diaphragm a squirt of WD40. Give it a wiggle and smile contentedly as you watch the clean, de-rusted iris moving freely. Have a cup of tea then contemplate how you’re going to tackle the rest of the microscope.
EDIT: Please see comments section for helpful advice regarding WD40 and oil on iris diaphragms.
Thanks to Merv Hobden for his advice and guidance.
http://www.picreator.co.uk/articles/1_about_us.htm
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