PDA

View Full Version : Rainbow finish on tools ..HOW ?



aboard_epsilon
10-18-2009, 09:27 AM
Here you see one of the surface gauges / scriber i bought today
can anyone tell from looking at ..from what is left of the original rainbow finish

how this rainbow effect is done ..or has it just acquired that patina somehow.

http://img.photobucket.com/albums/v190/aboard_epsilon/toolfionish1.jpg

http://img.photobucket.com/albums/v190/aboard_epsilon/toolfinish2.jpg

all the best.markj

Evan
10-18-2009, 09:33 AM
You should ask in the gun making forum. It's an effect from hardening.

gb25
10-18-2009, 09:48 AM
http://www.google.com/search?source=ig&hl=en&rlz=&=&q=color+case+hardening

Also:

http://bbs.homeshopmachinist.net/showthread.php?t=34425

MickeyD
10-18-2009, 09:53 AM
Usually the patterns like that came from a process called cyaniding, which involved dipping the heated parts into a bath of molten salt/cyanide broth - not very environmentally friendly. It is not done much anymore because of the problem with disposing of the wastes. Case hardening can give a similar pattern but is much harder to do and is generally only reserved for expensive (relatively) items like guns, knives, etc., where the customer will spend money for a certain "look".

nheng
10-18-2009, 10:00 AM
It comes from case hardening with a charcoal from wood and bone. Beautiful finish on some old Starrett stuff like this wiggler from the family jewels:

http://img.photobucket.com/albums/v319/nheng/misc/starrett65.jpg

In the US, Brownells has all sorts of kits and replenishables for doing it:

http://www.brownells.com/.aspx/cid=0/k=case+hardening/t=P/ksubmit=y/Products/All/search=case_hardening

aboard_epsilon
10-18-2009, 10:12 AM
thanks guys ..sounds a no go area to me ..no resources to do that

i was imagining that it was produced by the oil paints/ inks on water, 1 molecule thick surface tension method.

all the best.markj

lazlo
10-18-2009, 10:27 AM
It comes from case hardening with a charcoal from wood and bone.
In the US, Brownells has all sorts of kits and replenishables for doing it:

I posted a question about this about a year ago: when I do casehardening with Kasenit, it turns out flat.

A famous gunmaker replied with source for the powdered bone and the ultra-fine charcoal, explaining the relative mixtures to get the different colors. He also posted a bunch of pictures, which were stunning.

I love those old Starrett casehardened hand tools (they're all black oxide now). I think Starrett was still doing casehardening as recently as the 90's. At least, I have a NOS "modern" surface gauge that has the beautiful case hardening.

loose nut
10-18-2009, 11:16 AM
Generally referred to as "Color case hardening"

uncle pete
10-18-2009, 11:21 AM
One of the Machinist Bedside Reader books by Guy Lataurd gives directions on how to do this at home useing HSM methods.

Pete

lazlo
10-18-2009, 12:56 PM
One of the Machinist Bedside Reader books by Guy Lataurd gives directions on how to do this at home useing HSM methods.

Ironically, that was the reason for my previous thread :)

Barium carbonate toxicity? (http://bbs.homeshopmachinist.net/showthread.php?t=28292&)


The nitriding discussion got me thinking about trying the carburizing formula that Guy Lutard describes in the 2nd Machinist's Bedside Reader: bone charcoal + barium carbonate.

This is an ancient recipe that creates the beautiful rainbow oxide swirls that you see on old Starrett hand tools. I've used Kasneit, and it does make a hard case, but it doesn't color the metal very much.

Since barium is one of the alkaline earth metals (beryllium, magnesium, calcium, strontium, barium and radium are the others) how toxic is it?

Lutards' instructions just indicate that you drench the bone charcoal in the barium carbonate, pack air-tight in a clay container, and bake at 1650įF for an hour or so. I would imagine that there's not a lot of opportunity for any gases to escape, but I also have a 6 month old son in the house...

Any experiences with this stuff?

By the way, the barium carbonate apparently accelerates the absorption of carbon from the charcoal into the steel.

lazlo
10-18-2009, 12:58 PM
Mike Hunter was the famous gunsmith that replied with a simple home-shop formula for color case-hardening.

Look at his work on his web page. Amazing!

www.Hunterrestorations.com


For you folks that want to try this at home....

Go to Wal Mart, pick up some hardwood lump charcoal and some Bone Meal from the gardening section. Crush up the charcoal; throw in some bone meal, and yes cooking bone meal stinks to high heaven.

My initial CCH was done in this manner ... just a test to see if I wanted to invest the time and money into doing this.

It’s not cheap to set up properly, and it took me about 2 years to be able to get consistent results. Remember I do this for profit not fun..on other people’s parts, so if I ruin a part ie..warp a very expensive frame ..I've got to fix it or I just bought it...

There's an old saying "A amateur keeps practicing until he gets it right...a professional keeps practicing until he can't get it wrong"

I could not afford to get it wrong.

Henry.. nice work.. glad that you are teaching it.

Mike Hunter


http://www.hunterrestorations.com/RT_RCVR_after.gif

Evan
10-18-2009, 02:34 PM
You can achieve a very similar effect by selective application of heat with a torch after case hardening with Kasenit. Clean the case hardened piece to bare metal and then play the torch on it to bring out colour.

It will also work on pieces that are not hardened like this chunk of steel I engraved. In this case (!) I wanted an even effect, not swirls.

http://metalshopborealis.ca/pics4/harley2.jpg

aboard_epsilon
10-18-2009, 02:49 PM
isn't there a way to fake it ..without involving any heat ..


when i first saw the the finish ..like i said ..i thought of the old paint or ink floating on water trick .

all the best.markj

Mcgyver
10-18-2009, 03:23 PM
Usually the patterns like that came from a process called cyaniding, which involved dipping the heated parts into a bath of molten salt/cyanide broth - not very environmentally friendly. It is not done much anymore because of the problem with disposing of the wastes. Case hardening can give a similar pattern but is much harder to do and is generally only reserved for expensive (relatively) items like guns, knives, etc., where the customer will spend money for a certain "look".

small point, but cyaniding is a case hardening process, its not carburizing, but still a form of case hardening. i remember doing it in high school on a tack hammer head :)

oil mac
10-18-2009, 03:26 PM
I remember some years back, the toolmakers doing some hardening, where by, they packed steel components in a tube of cast iron, I think they may have packed the components in charcoal (cant remember the details) This tube was fitted with an inlet &outlet small pipe, through which nitrogen gas was passed
The benefits were that the components were not heated to an extremely high temperarure, I believe this system gave a nice finish to the surface also Anyone know any details of this process?

Evan
10-18-2009, 04:43 PM
It's called Carbonitriding. It produces both a carbon case and a nitride case at once.

Kasenit does the same thing. Sodium ferrocycanide contains equal amounts of carbon and nitrogen and so produces both a carbon and nitride case.

nheng
10-18-2009, 06:52 PM
I recall seeing a Discovery (??) channel show back when we first entered Afghanistan. In a dusty, isolated marketplace, there was a bread maker in one stall. In the next stall was an old man sitting behind a small round can buried in the ground, maybe 10" diameter and with embers inside. He was feeding strips of dried leather into it. There appeared to be other objects standing vertically in the packed can.

What a surprise it was to discover that he was case hardening AK47 receivers :eek: :eek: !

beanbag
10-18-2009, 06:59 PM
I haven't seen any of these "rainbow finish" effects in person, but IMHO it looks kind of tacky. Like the puddles in the parking lot of Walmart.

clutch
10-18-2009, 07:08 PM
Ironically, that was the reason for my previous thread :)

Barium carbonate toxicity? (http://bbs.homeshopmachinist.net/showthread.php?t=28292&)

I think I asked about that a year or two ago. I still have the barium carbonate sealed in the shipping container.

I haven't read in any of the metalworking forums about anyone damaging their health using Guy's description so I'm leaning towards trying this some day soon.

Clutch

lazlo
10-18-2009, 10:53 PM
I haven't seen any of these "rainbow finish" effects in person, but IMHO it looks kind of tacky. Like the puddles in the parking lot of Walmart.

If you see it in person, it's gorgeous.

lazlo
10-18-2009, 10:55 PM
I haven't read in any of the metalworking forums about anyone damaging their health using Guy's description so I'm leaning towards trying this some day soon.

What worried me about Luatard's article is that the first book he was quoting the Bullseye Recipe third-hand. I *think* that was the 2nd Bedside Reader. Then in the Third Bedside Reader, he notes that a chemist wrote-in saying the barium carbonate was dangerous when vaporized. Guy added a non-committal warning (something like - "Watch Out!"), but it left you wondering if it were safe or not.

Evan
10-18-2009, 11:24 PM
Re barium carbonate a quick check of the pysical properties show that it poses no special threat when vaporized. It doesn't decompose until it's boiling point of 2372F which is well over any usual heat treating temperature and when it does decompose it reverts to elemental barium and carbon dioxide.

In dust form it is insoluble in water but toxic if inhaled or swallowed for the same reasons that sodium bicarbonate and potassium compounds are. It upsets the body's acid/base balance and can cause convulsions and even death if enough is absorbed. Don't eat or breath the material.

beanbag
10-19-2009, 12:35 AM
If you see it in person, it's gorgeous.

Now that I think about it, I saw it on an end mill once, and it was quite nice. But then again, the base "color" was a shiny silver.

boslab
10-19-2009, 04:07 AM
must admit it didnt look like CN hardening to me, i,ve only ever seen a kind of pearl finish after the bath, looked like age an oil!, dont think Starret ever advertised surface guages with 'rainbow' finish!, not exactly repeatable or consistent.
My thoughts only [apart from never seeing strange colours out of the CN bath, never liked the cabinets on the wall, 'Break glass for antidote, a bloody big syrnge with antidote for cyanide poisoning 'solutions A and B' (ferrous sulphate dissolved in aqueous citric acid, and aqueous sodium carbonate)
think we had bottles of amyl nitrate at one time but they decided it might give you a heart attack]
it is a nice finish however it got there!
mark

lazlo
10-19-2009, 05:02 AM
Re barium carbonate a quick check of the pysical properties show that it poses no special threat when vaporized.

Read the thread. Several knowledgeable people pointed out serious safety concerns, as did Guy Lutard.

Evan
10-19-2009, 05:32 AM
I'm going by the MSDS which normally tends to exaggerate the safety issues. They don't show much to be concerned about as long as normal precautions are taken the same as you should using Kasenit or similar materials. Kasenit is probably more dangerous in that respect as it does evolve small amounts of cyanide gas as it decomposes on the workpiece. I always use a fan behind me or do it outside with the breeze at my back.

lazlo
10-19-2009, 05:44 AM
As a solid, it's safe. The issue is that it's vaporizing during the heat treat process.

From my original thread:

http://bbs.homeshopmachinist.net/showthread.php?t=28292&page=3




Lazlo,

All of the info you need is in the msds. You have to be able to read beyond the lawyerese to the physical and chemical properties. The BARIUM CARBONATE you wish to use starts out as a solid, generally the easiest hazmat category to work with. If you look under section nine, alot of info is in those couple of lines. The vapor pressure is listed as "0" at 68 Degrees F. Atmospheric pressure is approximately 760 mm/hg at 68F. What that tells you is that the material is not going to be releasing relatively any vapors at 68F. As far as routes of exposure, inhalation is generally the hardest for the layman to protect against. Ingestion is relatively easy as far as protection, do not eat the material or get it on something that you put in your mouth. A cigarette or food and drink make excellent vectors for exposure. Contact as far as a liquid or solid is generally protected by using gloves, suits, etc.

You propose to heat the material thus dramatically changing the situation. If we refer to the msds again under section 9 and look at the boiling point we are given a value of 1492 F. This value is below the temp that you propose to heat the material to. When heating the material you can expect the solid to melt to it's liquid phase and become mobile. The vapor pressure will increase and vapor production will increase. If heated to 2372F you will have a gas as opposed to a solid or liquid.

To compare this to something you are hopefully familiar with take a look at acetone. The vapor pressure is 180 mm/hg at 68F. Although not at it's boiling point of of 133F, there is still adequate vapor pressure that you can smell it at room temp. If you can smell it, you are inhaling it if you are not protected.

If it was me, I would not take a chance on exposing a young child or myself to this. I work with toxic and exotic chemicals for a living and you evaluate the risks and determine what is acceptable, legal, and moral. If it was to remain in a solid state of matter, I personnaly would put on compatible gloves and work away. Change the equation with the addition of heat and I would not work with this material in a residential setting. As far as a lab the minimum would be fume hood with splash protection due to the solid melting and becoming mobile/vaporous.

Rick

lazlo
10-19-2009, 05:47 AM
http://bbs.homeshopmachinist.net/showpost.php?p=344810&postcount=24




Thanks Joe -- the usual MSDS stuff doesn't help very much:

11. Toxicological Information

Oral (Rat) LD50:418 mg/kg Investigated as a reproductive effector.

Just FYI: The "LD50:418 mg/kg" means that the Lethal Dose for 50% of the population is 418 mg/kg. So if you have 100 standard 1 kg lab rats and you feed them each 418 mg then you can espect 50 of them to croak. They use 50% of the population because a few of those little suckers will thrive and get fat on Barium or DDT or Xylene or whatever you're testing.

And I agree with the other poster that said you don't really want to mess with heating it to melting at home. Using it for rat poison, where you would handle a small amount and then wash your hands is a different matter.

Mike

Evan
10-19-2009, 06:44 AM
The issue is that it's vaporizing during the heat treat process.


There are some unwarranted assumptions and poor analogies in that post. Acetone and molten barium carbonate are not similar or equivalent. There is no particular reason to assume that liquid barium carbonate has a high vapour pressure regardless of temperature below boiling. It's a metallic hydrated oxide, not a volatile organic compound. Metallic oxides do not have a tendency to evaporate when molten until the boiling temperature is reached.

see here: http://origin.cdc.gov/niosh/docs/81-123/pdfs/0045.pdf

The recommended practise (not required practise) for use in heat treating is a process enclosure with simple ventilation, nothing more. In other words, stand up wind. Cleanup after use is to wash hands with soap and water.

aboard_epsilon
10-19-2009, 09:11 AM
I posted a question about this about a year ago: when I do casehardening with Kasenit, it turns out flat.

A famous gunmaker replied with source for the powdered bone and the ultra-fine charcoal, explaining the relative mixtures to get the different colors. He also posted a bunch of pictures, which were stunning.

I love those old Starrett casehardened hand tools (they're all black oxide now). I think Starrett was still doing casehardening as recently as the 90's. At least, I have a NOS "modern" surface gauge that has the beautiful case hardening.

if you look close enough at the second pic down ..it is a starrett.,..not Moore and wright as i originally thought ..the bigger one is the M&W..which also has the rainbow colouring ..

its just that every tool Ive found up to now has been so rusty that it couldn't be seen.

all the best.markj

Mike Hunter
10-19-2009, 11:30 AM
As Lazlo pointed out, I do a lot of Color Case Hardening here in the shop. Case Hardening provides a hard wear resistant outer surface to low carbon steel, usually the case is only a few thou thick. Color Case Hardening (with the beautiful mottled colors) has been done for hundreds of years using only bone & wood charcoal, and I suspect most of the old tools were done that way.
No real need for cyanides, barium carbonate etc. Iíve tried a couple of these compounds (less cyanide) in and found no appreciable benefits

Mike Hunter.

Evan
10-19-2009, 11:45 AM
Bones contain calcium carbonate. Close enough. Calcium is also a metal although never found in the native state.

lazlo
10-19-2009, 01:05 PM
Mike, do you have a source for small quantities of bone charcoal?

Brownell's sells 25 lbs for $109, and I can never use that much.

Apparently "bone char" is the same stuff, it's used for art pigment, but it's about $28/lb (!)

camdigger
10-19-2009, 01:52 PM
Isn't "bone char" simply cooked "bone meal" available at your local garden center?

I seem to recall as part of my reading somewhere that color casehardening involves bubbling air through the quench? If so, any carburizing soak should work...

lazlo
10-19-2009, 01:53 PM
Isn't "bone char" simply cooked "bone meal" available at your local garden center?

Yes, but everyone I'd spoken to says that it makes an incredibly nasty smell when you char bone meal.


I seem to recall as part of my reading somewhere that color casehardening involves bubbling air through the quench? If so, any carburizing soak should work...

I've done a bunch of pieces with Kasenite, and I don't get any coloring. I think it's the various organics in the wood and bone charcoal that give you the pretty colors.

Mike Hunter
10-19-2009, 02:06 PM
Lazlo, what are you wanting to do? I get my bone char 100 lb at a time. Do you want to try some home Color Case Hardening, if so Iíve got some used stuff that I can probably send you? Itís still good, I just have a different ratios of bone v wood that I use for different firearms (Colt v. Marlin v. Winchester) once dumped in the quench tank; I no longer have control over ratios.

As to the bubbling air, the primary purpose for the air is to circulate the water around the part, otherwise you may end up air pockets, this can cause soft areas, or extremely hard areas, cracking distortion etc.

JCHannum
10-20-2009, 05:46 PM
Mike's CCH is among the best. There is much more involved in obtaining results of this quality than simply cooking and quenching though. The basic materials are simple, bone and wood charcoal as mentioned, sometimes leather charcoal is added and most manufacturers had their own recipe and methods.

Temperature is critical as is length of time held and material of course. The parts must be quenched as quickly as possible, with minimal contact with the atmosphere. The air sparging of the quench tank does also seem to have an effect as some colors seem to display paths that the bubbles might have taken during the quench process.

This is a link to an experimenter that details what he went through to replicate the colors found on Marlin receivers. It was 17 pages the last time I looked, but it continues to grow as information is added from others.

http://www.marlin-collectors.com/forum/viewtopic.php?f=21&t=3732&st=0&sk=t&sd=a

Some coloring can be achieved with torch work, but they are phony and are easily detected as fake. They do not last as long as real CCH either and can draw the temper from what was initially a properly case hardened part.

camdigger
10-20-2009, 05:55 PM
Some coloring can be achieved with torch work, but they are phony and are easily detected as fake. They do not last as long as real CCH either and can draw the temper from what was initially a properly case hardened part.

That whole torch coloring thing is related to colors of oxidation used to judge surface temperatures when tempering steels after the initial quench isn't it? The color of oxidation is an indication of surface temp and as such is obviously going to affect any previous tempering...