Photoetch brass black problems

[Seems ok to me]

Having primed and painted photoetch in the past only to have the paint flake off at the merest breath of a scratch, I am trying brass black on this bunch. Needless to say, the results are less than spectacular.  
 

My steps:

-clean with acetone wearing gloves

- dunk in fresh brass black (using birchwood Casey) for a few minutes

-rinse in cold water, let dry. 
 

The main problem is poor coverage even when I repeat the blackening. The stuff seems to just wipe off and leave black dust all of the place.  Some also developed a grayish hue.  Any tips?  What am I messing up?  
 

 

[Snug Harbor Johnny]

Perhaps the surface needs some 'tooth' prior to finishing - a careful rubbing with ultra-fine sandpaper (600 grit? there are some finer than that).

[Beef Wellington]

I would suggest diluting the solution more, the flaky finish seems to be common when the concentration is too strong resulting in an overly fast reaction - at least from my experience...

[BANYAN]

Hi [nickname?]

 

I have been doing both methods of finishing PE you mention for some time, and this response reflects my experiences only - may be alternate answers forthcoming

 

The brass stock used with PE is sometimes covered with a protective coating, or has some residual chemical coating, that needs to be removed.  I find that cleaning with a fibre scratch pen (like a propelling lead pen) helps greatly, especially if the PE is to be soldered also.

 

If painting, I also found that using a metal etch solution (such as those from Mr. Metal) helps the paint adhere.  Even if well cleaned and undercoated with a good quality primer, without such a metal etchant, I also experienced the same scratching issues.

 

If blackening, here cleaning is very important.  I also scratch clean with the fibre pen for this process to ensure I remove the coating.  Your cleaning is OK I think, but the main issue I see here is the strength of the blackening solution you are using.  I have found it is better to use a diluted solution.  I start with a 50/50 demineralised water/birchwood casey blackening solution; however, with some metals an even weaker solution creating a 'slow baked' patina gives a better result..  I usually give the part about 5 minutes in the first dip then check progress.  Even with the best cleaning sometimes, parts of the PE fail to take the patina initially.  If I see areas not blackening, while still wearing rubber gloves - nitro type, not the powdered ones) I give the affected areas another clean with the scratch pen.  You have to be careful with PE as you have probably found already, some parts are very delicate.  It is then put into the blackening solution, then checked again after a few minutes.  Sometimes I have had to do this three times.

 

The results I get are a nice grey iron like  patina initially.  The longer, and more often you put the parts into the diluted solution provides a deeper colour.  Between baths, once I have a full coverage, I wipe/polish with a paper towel to see what the depth of colour is.  Once happy with the colour, rinse well under flowing fresh water and polish dry.

 

I hope this works for you.  Happy modelling.

 

Pat

Edited January 27, 2021 by BANYAN

[dvm27]

Perhaps check out this tutorial which seems to work for me and some others: https://modelshipworld.com/topic/21710-blackening-revisited/?tab=comments#comment-651453

[Seems ok to me]

Thanks for all the replies. It didn’t even occur to me to dilute the solution. The reaction speed could be an issue as I have a bunch of black grit come off as soon as the parts hit the solution. I had been using 00 steel wool to rough up the surface but doing much of a job on a tiny 5mm bits of brass was challenging to say the least. I will check out the link above as well. Thanks to all. 

[Seems ok to me]

Follow up:

Now that I’ve made a mess of things, could I clean these parts somehow and start again with the techniques above with any hope of success?  

[BANYAN]

I have done that many times.  I used the scratch pens to do that, but a thorough clean is needed.  I have tried the Sparex, but found it did not work so well for me (could be technique etc).  I have used a Ultrasonic cleaner but it is not necessary.

 

cheers, and good luck.

 

Pat

[cog]

On 1/28/2021 at 12:38 AM, Snug Harbor Johnny said:

Perhaps the surface needs some 'tooth' prior to finishing - a careful rubbing with ultra-fine sandpaper (600 grit? there are some finer than that).

Tamiya, has sanding sponge sheets you can use for that. 2000 or 3000 grit should do it

[wefalck]

Too high concentration has a similar effect to leaving the part too long in the solution: the chemically altered layer on the surface is porous and the reaction continues underneath with the effect that the first formed layers flake off.

 

As Pat said, taking the piece out frequently, rinse it and check progress is a good strategy to stop the process just at the right moment. Depending on the blackening product used and the brass composition, it may take only a few tens of seconds actually.

[AJohnson]

Thanks all for the tips above, I am having just this problem and think now, having read the above I am leaving the PE in too long and certainly haven't diluted the blackener.  So will try as suggested for the next batch of hooks and chain plates.

 

Thanks again! 😁

[bartley]

See my comments ion this thread  here and elsewhere on this site. Wefalck is correct  prolonged exposure or too strong a solution is the culprit.  If you dilute the reagent 1:1 good blackening should occur in 30  seconds  If it takes longer than this then the surface is not clean enough.  You need to use acetone to remove laquer coating and pickling to remove oxide from the surface.  See this example.

 

John

[javajohn]

I'm curious if anyone here has tried using fret erasers to clean photoetch before blackening it? Fret erasers are rubbery erasers with grit mixed in that are used to polish frets on guitar fingerboards. I had some photoetch that was badly tarnished and scratched. All I had on hand was some fret erasers and they worked great.

 

John

[allanyed]

These erasers may work, but personally I have never found a better system than the one described by Greg at     

https://modelshipworld.com/topic/21710-blackening-revisited/?tab=comments#comment-651453    It is a fail safe method. The pickling will give you the "rough" clean surface.  An eraser like you describe by itself probably will not work without pickling so may as well skip the eraser as it will not add any advantage to this system.   The only problem in the write up is I that I have not been able to find Blacken It for a couple years as I am pretty sure it is no longer available.   Birchwood Casey is probably the next best solution to use, although I find a dilution of about 3 or 4 to 1 works better than 7 to 1 for this particular product. 

 

Allan

[kurtvd19]

Blacken it is no longer made.  It was a small business - husband and wife - they were killed in a car accident a few years ago and the company died with them. 

[javajohn]

@allanyed I will have to try that technique. The results look more like a professional blackening then what I ended up with using the erasers. I still had a tiny bit of flaking. The pickling sounds like that is a key to preventing flaking.

 

John