About 3 years ago I set up a small metal bluing tank bluing and posted a few details a a couple of photos in this post.
http://ift.tt/1SbRKKV
Since then I have blued some small pieces, and have also have received a few PMs about what I do.
What I have been meaning to do for a while is post a few more details of the process and include some more pics.
The pieces I am bluing are the bearing housing, wheel collar/flange and table hold down screw for the thin kerf cut off saw I made a couple of weeks back.
This is the bearing housing - not the best bit of machining but it works and it's done now and that's what I have to work with.
The recipe I used was almost identical to what I have posted before but here it is again but this time with pictuires.
1) Polish the metal to as high a shine as you desire for the final finish.
The smoother the finish the more reflective and protective the coating will be.
Mine have only been polished using a scotchbrite wheel so it was more of a matt polish.
Sorry no pics of this stage
2) Wash the oil and gunk from the metal parts by boiling is a weak (5%) solution of sodium carbonate [(Foot spa salts) a 500g bag costs about $5 a bag at coles] for an hour
3) From this point onwards handle the parts with rubber gloves. I use those disposable latex type.
Rinse the parts with distilled water and suspend pieces in the bluing chamber from pieces of wire.
Make sure the chamber is sealed to keep in the fumes or they will corrode all ferrous stuff they come into contact with.
The bluing chamber contains two open containers one with concentrated HCl and the other with concentrated HNO3.
4) After the parts have formed a coating of rust [this can take anywhere from a couple to 12 hours] remove from chamber
This is they look like after the 4th pass, after the first pass they come a much brighter orange (i.e. rust)
5) Place the rusty looking pieces into a clean container of fresh, boiling distilled water.
I use a large clean stainless steel saucepan on an old electric frying pan and hook the pieces onto the side of the saucepan.
Boil for ~one hour, rust colour should go black.
6) Remove and allow parts to dry.
This is typically how they look after boiling
It doesn't matter if they are patchy, underneath that grey colour on the large middle piece will be a black sooty layer of black oxide.
7) Then remove the loose "soot", which is black iron oxide,from all surfaces using a fine stainless wire brush and/or fine steel wool.
Fine steel wool works well on flat surfaces but brushes will work better on threads and into nooks and crannies.
The amount of soot that comes off looks like you are taking it all off but that is normal.
Rub hard enough to achieve a smooth surface but not so hard as to get it back to bare metal
This shows the amount that comes off 0 quite a bit and make a mess hence the need for gloves.
After the first pass through the bluing tank the steel might only have changed to a medium grey like this but this is entirely normal .
8) Repeat steps 3 - 7 until the desired depth of colour and protection is obtained.
This means somewhere around 10 passes.
Here's what they are looking like after 5 passes (NB the soot has been removed before the photo was taken)
They look nice and black in the photo but more cycles will make a more lustrous bluer hued colour that is more protective. This batch is going dark a lot quicker than usual - i think it may be because I have been a lot more careful about keeping things clean, i.e. double rinsing the saucepan after every pass etc.
It is interesting to see the pieces slightly change colour hue after every few cycles. first they are grey, then dark brownish and then faintly blue and then full on black.
After 5 cycles I now switch to superfine steel wool
9) finally Heat the parts in hot oil (I use new engine oil in another stainless steel saucepan on the electric frypan) for a couple for hours. Remove parts from oil, let cool and wipe off excess oil. For maximum protection the parts should be kept lightly oiled. If they develop surface rust they can be re-blued as per new pieces.
Thats it.
It's a very slow process but the finish is supposed to be one of the more robust of the bluing methods. It's not used much because it is so slow.
http://ift.tt/1SbRKKV
Since then I have blued some small pieces, and have also have received a few PMs about what I do.
What I have been meaning to do for a while is post a few more details of the process and include some more pics.
The pieces I am bluing are the bearing housing, wheel collar/flange and table hold down screw for the thin kerf cut off saw I made a couple of weeks back.
This is the bearing housing - not the best bit of machining but it works and it's done now and that's what I have to work with.
The recipe I used was almost identical to what I have posted before but here it is again but this time with pictuires.
1) Polish the metal to as high a shine as you desire for the final finish.
The smoother the finish the more reflective and protective the coating will be.
Mine have only been polished using a scotchbrite wheel so it was more of a matt polish.
Sorry no pics of this stage
2) Wash the oil and gunk from the metal parts by boiling is a weak (5%) solution of sodium carbonate [(Foot spa salts) a 500g bag costs about $5 a bag at coles] for an hour
3) From this point onwards handle the parts with rubber gloves. I use those disposable latex type.
Rinse the parts with distilled water and suspend pieces in the bluing chamber from pieces of wire.
Make sure the chamber is sealed to keep in the fumes or they will corrode all ferrous stuff they come into contact with.
The bluing chamber contains two open containers one with concentrated HCl and the other with concentrated HNO3.
4) After the parts have formed a coating of rust [this can take anywhere from a couple to 12 hours] remove from chamber
This is they look like after the 4th pass, after the first pass they come a much brighter orange (i.e. rust)
5) Place the rusty looking pieces into a clean container of fresh, boiling distilled water.
I use a large clean stainless steel saucepan on an old electric frying pan and hook the pieces onto the side of the saucepan.
Boil for ~one hour, rust colour should go black.
6) Remove and allow parts to dry.
This is typically how they look after boiling
It doesn't matter if they are patchy, underneath that grey colour on the large middle piece will be a black sooty layer of black oxide.
7) Then remove the loose "soot", which is black iron oxide,from all surfaces using a fine stainless wire brush and/or fine steel wool.
Fine steel wool works well on flat surfaces but brushes will work better on threads and into nooks and crannies.
The amount of soot that comes off looks like you are taking it all off but that is normal.
Rub hard enough to achieve a smooth surface but not so hard as to get it back to bare metal
This shows the amount that comes off 0 quite a bit and make a mess hence the need for gloves.
After the first pass through the bluing tank the steel might only have changed to a medium grey like this but this is entirely normal .
8) Repeat steps 3 - 7 until the desired depth of colour and protection is obtained.
This means somewhere around 10 passes.
Here's what they are looking like after 5 passes (NB the soot has been removed before the photo was taken)
They look nice and black in the photo but more cycles will make a more lustrous bluer hued colour that is more protective. This batch is going dark a lot quicker than usual - i think it may be because I have been a lot more careful about keeping things clean, i.e. double rinsing the saucepan after every pass etc.
It is interesting to see the pieces slightly change colour hue after every few cycles. first they are grey, then dark brownish and then faintly blue and then full on black.
After 5 cycles I now switch to superfine steel wool
9) finally Heat the parts in hot oil (I use new engine oil in another stainless steel saucepan on the electric frypan) for a couple for hours. Remove parts from oil, let cool and wipe off excess oil. For maximum protection the parts should be kept lightly oiled. If they develop surface rust they can be re-blued as per new pieces.
Thats it.
It's a very slow process but the finish is supposed to be one of the more robust of the bluing methods. It's not used much because it is so slow.
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