The power of oxalic acid to remove rust

I was very excited to obtain a second hand trinocular head for my Zeiss IM microscope. However, when I took the phototube off the head, I wasxshocked to find it rusted inside- this was on both the phototube and head where they attached to each other.

The picture below shows the rust on the head. The good news is that this is the only place with rust. I took the head apart and there is no rust inside. So, I guess moisture has just got into this bit which was made of unprotected steel. The sellers are unlikely to have known it was there as I doubt they ever had reason to take the phototube off the head.

My wife suggested I do some research on the internet to find out the best way to remove this rust. I came up with italic acid as a particularly powerful rust remover, although with warnings to open windows due to the fumes. This sounded like the beasty I needed so I ordered some from the all-encomposing ebay. It arrived last week so I had a go this weekend at using it to remove the rust.

I started with phototube. This is just a simple metal tube so there are no optics to ruin. I prepared the italic acid solution – a few teaspoons in hot water stirred with an ice lolly stick (I did not want acid to ruin our household spoons!) I then prepared a shallow glass container of the acid  (I did not know whether the acid would burn through plastic although I suspect it would be OK as the italic acid crystals were sent in a plastic container).

The following picture shows the container plus the amazing result of sitting the phototube is the acid for only a couple of minutes. The rust just disappeared as if by magic! Immrsion in this acid is very effective. A good wash under the tap followed to wash off the acid then 30 minutes in the oven at very low temperature to dry it out thoroughly so it did not immediately rust again. A light covering oil finished the job.

I then tackled the trinocular head itself. I used some tissue to cover the lens just below the dovetail joint, to minimise the chance of getting acid on it and then an old toothbrush to gently apply acid and rub it off again.

Immersion and running water over it and ovens were not going to be possible for this piece!

I was equally amazed to see the effect if applying a small amount of italic acid with the toothbrush. This also instantly lifted the rush coat. Wow!

The following pictures shows the final results. In this picture, the dovetail on the head still looks a little rusty but in reality it is actually quite clean of rust. I had difficulty showing this well in the photograph

I have a few rusted screws on my 16 inch Lightbridfe from when I kept it in an unheated, non-dehumidified environment that will look a lot better after some oxalic acid…

The following pictures show the trinocular head and it’s phototube – both are unoriginal Zeiss. I am not sure of the model number not which scope it was originally made for.


The following photo shows the trinocular microscope in the configuration uses on the microscope. Here, the Diagnostic Instruments 0.7x adapter is attached to the Zeiss phototube. The DI adapter itself has a c-mount attachment and I have used c-mount to t-mount adapter followed by a t-mount threaded 2-inch eyepiece adapter and a 2-inch to 1.25 inch eyepiece adapter. This configuration allows me to use my Bresser MikrOkular camera in the trinocular head’s camera port.

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