Mantua "blue painted" photo-etched brass

[Alexisgm97]

Hello,

I have recently bought the Royal Caroline kit by Mantua and as it is a quite old model (I got it at a very good price from second hand although everything is new) some parts that are now made of thin wood are a photo-etched brass sheet. See the images below to see what I mean, please.

 

 

 

Here you can see the wood parts that come with the new version of the model (The photo is from Katsumoto's build log found here).

 

However, in the old kit I bought, this same part is made of a brass sheet and it has a blue colour on the embossing, which I imagine is to protect it against scratches or oxidation as we all know brass tends to get a brown colour very fast.

 

 

So my doubt is, how do I remove this blue colour without damaging the brass too much? Mantua's instructions say that it can be removed with sand-paper but I'm afraid it can be too abrasive and mess it up.

 

I hope you can give me some advice on how to remove this blue paint without damaging the brass and give it a really good finish.

 

Thanks and stay safe.

Alexis G.

[PietFriet]

Not an answer to your question but maybe an alternative to consider. The wood version is separately for sale for less than 20 euro. The article number is 44101.

[bruce d]

Hello Alexis,

The blue on the brass is left over from the etching process. It was called 'resist' and was the barrier between the etchant and the area of brass that was not to be etched.

You may be able to remove it without sandpaper but it is not possible to be certain without knowing exactly which product they used. The blue film was able to 'resist' the powerful etchants so of course it does not just peel off. There are 'etch resist strippers' available for people who make their own printed circuit boards but there is no guarantee that these modern products will work on this old blue product. Very few of the old products are still used because they used aggressive, nasty chemicals so modern resist uses different strippers.

Try cellulose thinners if you can, also the type of solvent used by plumbers to bond PVC tubing. If this doesn't work, I am afraid it is time to start sanding.

Good luck!

HTH

Bruce

[Dr PR]

One of the chemicals used for an etch resist stripper is sodium hydroxide (NaOH), a strong base/alkali. Caution: NaOH will cause skin burns and eye damage.

 

Since NaOH is a base, and is used to remove resist, acids probably won't work. Besides, acids will attack the brass.

 

Etchants are usually water based, so most water soluble solvents probably won't work (alcohol). First I would try acetone or enamel or lacquer thinner and an old tooth brush. These solvents won't harm the brass. If they don't work try sodium hydroxide.

[Gregory]

On 3/27/2021 at 6:49 AM, Alexisgm97 said:

Mantua's instructions say that it can be removed with sand-paper but I'm afraid it can be too abrasive and mess it up.

It's only too abrasive when it's too abrasive...

 

The grit on these start at 1500 and is used for polishing.

 

Grit 1500 2000 2500 3000 5000 7000 High Precision Polishing Sanding Wet/dry Abrasive Sandpaper Sheets - Germany, Pack of 12

[bruce d]

Please let us know how it works out for you.

[Alexisgm97]

On 3/27/2021 at 12:04 PM, PietFriet said:

Not an answer to your question but maybe an alternative to consider. The wood version is separately for sale for less than 20 euro. The article number is 44101.

I have alredy thought about that but I don't know why but brass appeals more to me. It is just my taste but that would be a good idea too.

 

Thanks

[Alexisgm97]

On 3/27/2021 at 12:34 PM, bruce d said:

Hello Alexis,

The blue on the brass is left over from the etching process. It was called 'resist' and was the barrier between the etchant and the area of brass that was not to be etched.

You may be able to remove it without sandpaper but it is not possible to be certain without knowing exactly which product they used. The blue film was able to 'resist' the powerful etchants so of course it does not just peel off. There are 'etch resist strippers' available for people who make their own printed circuit boards but there is no guarantee that these modern products will work on this old blue product. Very few of the old products are still used because they used aggressive, nasty chemicals so modern resist uses different strippers.

Try cellulose thinners if you can, also the type of solvent used by plumbers to bond PVC tubing. If this doesn't work, I am afraid it is time to start sanding.

Good luck!

HTH

Bruce

Hello, 

 

Thanks, I know it is made to resist different solutions so I think I will try acetone first because that's what I have got at home if it doesn't work I will have to go with sanding

[Alexisgm97]

15 hours ago, Dr PR said:

One of the chemicals used for an etch resist stripper is sodium hydroxide (NaOH), a strong base/alkali. Caution: NaOH will cause skin burns and eye damage.

 

Since NaOH is a base, and is used to remove resist, acids probably won't work. Besides, acids will attack the brass.

 

Etchants are usually water based, so most water soluble solvents probably won't work (alcohol). First I would try acetone or enamel or lacquer thinner and an old tooth brush. These solvents won't harm the brass. If they don't work try sodium hydroxide.

I see.

 

Thanks! I think I will try with acetone and see how it goes. The old brush with the acetone of course is also a good idea to try to remove it with something less agresive than sand paper.

 

Thanks

[Alexisgm97]

1 hour ago, Gregory said:

It's only too abrasive when it's too abrasive...

 

The grit on these start at 1500 and is used for polishing.

 

Grit 1500 2000 2500 3000 5000 7000 High Precision Polishing Sanding Wet/dry Abrasive Sandpaper Sheets - Germany, Pack of 12

Thanks! 

 

As I said I will try with acetone first but if it doesn't work or doesn't work properly the grit 1500 will be my second option. It can be used with water too right?

[bruce d]

 

 

16 hours ago, Alexisgm97 said:

the grit 1500 will be my second option

 

Alex, I would suggest using fine wire wool instead of sandpaper. Be patient and you will probably get a surface finish that will be ready for painting.

[James H]

Pretty sure the blue areas are the remaining photo-resist film from production (from my old days in circuit board manufacture). 

 

That should be easy to gently sand away, or even peel, depending on thee type of resist (ink or film).

 

When I built this model, I painted blue (I think) in the bare brass areas, then rubbed the parts over some very fine grade abrasive paper to reveal the brass, and then rubbed over finer papers until it was polished. I then sealed the brass with lacquer so it didn't tarnish. 

[Dr PR]

If you use very fine grit sandpaper (400 or better) and lay the sheet flat, grit side up, you should be able to rub the photo etch sheet over it to remove the resist without rounding the edges of the pieces.

 

Rubbing with #000 or #0000 steel wool will probably round the edges, and it can get tangled in the finer etched parts and bend them.

 

I remembered that the sodium hydroxide solution was used to remove  a pressed on resist film.

 

It doesn't take much on the surface of brass to block the etching solution. I used to make "printed" circuit boards by drawing the traces on the material with water proof Sharpie pens (laundry marker type). After etching acetone removed the ink.