Hybrid Stove Top Still - Build & Operation

[GingerBreadMan]

Introduction. I wanted to have a versatile still that could be used to make a variety of spirits from vodka to rum. My previous stills - (Version 2 and 3) were simple pot stills that I used to make rum, the latter version producing excellent results. However, I wanted to be able to make vodka for coolers. Not being a vodka drinker, I didn't need to have 95% purity, just needed a still so I didn't have to distill through my pot still three times.

Design Criteria. Living in an apartment space is a premium. The most important design criteria was space - this still has to be easily stored, setup and taken down and stored again. The second design criteria was safety of materials. I wanted a still made of only stainless steel and copper with no questionable materials - such as telfon tape or does the brass fitting have trace amounts of lead, etc. And finally the last design criteria was this still should be durable and last for years to come.

Description of still. The still uses a 12 quart stainless steel stock pot as a boiler and is heated on an electric stove top that has a maximum power setting of 1500 watts. A stainless steel bowl is mounted on top of the pot to provide 'head room' to prevent foam overs or 'puking'. A small 16" copper column (diameter 1 1/2") is attached to the bowl and raises straight up. Inside this column I can put structure copper packing when operating the still in fractionating or reflux mode. A copper tee is connected to the column to allow the vapors to exit and condense in a liebig condenser and mounted at the top of the tee is a small cold finger condenser to create reflux. The top of the column is closed as opposed to regular reflux columns (such as the bokabob) and the 'open to the atmosphere' safety feature of a still is done like a conventional pot still (no restrictions - open at the output).



Theory of Operation. The vapor path is marked by the red arrows. Vapor flows out of the boiler, goes out the tee and condenses (the dotted red arrow) in the liebig condenser. The cooling water flows from the bottom, through the liebig condenser and out the top as marked by the green arrows. With the reflux valve closed (circled in blue) this is the normal operation for pot still mode.

I can run the still in pot still mode with or without structured packing. By adding some packing to the column a bit of natural reflux will occur and this kind of still is known as a fractionating column.

When the reflux column (blue circle) is open then water flows through the cold finger condenser at the top as shown by the blue arrows. Alcohol vapor will condense at the top and drip down to the packing shown as the dotted yellow line. Purity increases (% alcohol content) and flavor reduces. The still is operating in column mode - great for making vodka and light flavored spirits.

[GingerBreadMan]

Building the still

I built this still entirely on my balcony - no workshop here - just me sitting on the balcony floor with a scrap piece of plywood (2 ft x 2ft) on the floor to protect the astro turf carpet. Here are the tools I used -

- Propane torch, brush for applying flux
- Soldering iron tip for propane torch (substitute electric soldering iron if you want)
- Electric Drill with an assortment of metal drill bits
- Dremel tool - cutting wheels, sander, SS brush tip
- Round bastard file - for filing away 'stops' when making liebig condenser
- copper pipe cutter
- pliers, screwdriver
- Leather Work gloves (for holding hot parts)
- Sandpaper, copper piper cleaner, steel wool, stainless steel scrubbers
- Latex gloves - a must when using steel wool to clean

I'll break down the build with photos covering the various sections of the still. However this is not a step by step, beginning to end illustrated process - Use your common sense, ie. don't solder the top of the column shut before putting in the cold finger condenser.

The Boiler

Materials
12 qt stainless steel stock pot
2 stainless steel bowls - matched to fit the diameter of the pot
1 1/2" copper pipe end cap
1/4" stainless steel bolt and nut with 2 washers
8 binder clips (medium 1 1/4" in size)

Soldering and assembling the boiler is covered here -

How to Solder

Read carefully all posts - there is lots of good information on how to solder using normal plumbing solder the stainless steel - in other words - this is not silver soldering, welding or brazing.

The vapor path

Materials needed
16" of 1 1/2" copper pipe (A)
5" of 1 1/2" copper pipe (B)
Copper Tee - 1 1/2 x 1 1/2 x 3/4 (C)
1 1/2" copper test cap (D)
1" of 3/4" copper pipe (E) (to join the two tees together)
Copper Tee - 3/4 x 1/2 x 3/4 (F)
20" of 1/2" copper pipe (G)



Don't solder all parts together - wait until the you put the cold finger together before soldering B, C & D (the top of the column). After you have soldered A,C,E,F,G it's really good time to clean the inside with steel wool and water and vinegar to get rid of all the extra flux. Everything is open for easy access.

Second note: Solder A & C last, you might even want to wait until the liebig condenser is soldered on. Once the big diameter copper is soldered, it becomes harder to heat up the solder joints because all that copper will 'wick' away the heat. Soldering 1 1/2" copper with a single propane torch will take some time. I probably had to heat up the pipe for a good 5 minutes before the solder would start to flow. A hotter torch or a second torch held by a friend might make this job easier.

Length and angle of output arm: Since the output arm (G) is connected to the column with two tees the angle it flows downward is variable. The 20" inch suggested is the minimum for 1500 watts of power. You can choose a longer length and any angle you want. The basic idea is to have the distillate output away from the stove while trying to keep the angle a bit steep so most of the weight of the output arm is over the pot- preventing it from the tendency of 'tipping'.

Liebig condenser

Materials
2 brass 1/2" unions (A,G)
2 Copper Tees 1/2 x 1/2 x 1/2 (B,H)
4" of 1/2" copper pipe (C)
Brass water valve (solder type) (D)
5" of 1/2" copper pipe (E)
1/2" to 3/8" OD copper reducer (F,I)
2 Copper Tees 3/4 x 1/2 x 1/2 (J, L)
16" of 3/4" copper pipe
5 copper pipe sections 1/2" to attach A-B, G-H, H-I, B-J, H-L



The liebig condenser consists of two basic functional parts. The 3/4" pipe and reducing tees (J,L) slide over the output arm to cool the vapors back to liquid. The other portion connects to the cooling water supply and also to the cold finger condenser at the top of the column.

The reducing tees (J,L) will have stops that prevent a 1/2" pipe from sliding through the tee. These stops will have to be filed out so the output arm of vapor path can slide though the tee. I used a round bastard file to file out these stops. This can be done quickly, about a minute of filing to remove the copper.

The water shut off valve (D) is a simple solder in brass valve. The soldering instructions state that the valve should be soldered with the valve in the open position and you should wait until the components have cooled down before turning the valve. The valve will open and close in a 1/4 turn so this valve is not chosen for fine adjustments, but rather a basic off/ fully on adjustment - see operating instructions on how to use the still.

Lengths and other stuff: The length of the pipes and the angles the copper tees (B,H) are not critical, I chose these as they represented the minimum length for cooling distillate with a heat input of 1500 watts and they made sense for connecting the cold finger condenser at the top.

After the stops have been filed out you can solder the liebig to the vapor path.

Cold Finger Condenser

Materials
2 Copper End caps 3/4" (A/C)
5" of 3/4" copper pipe (B)
2 short lengths of 3/8" OD copper tube (D,E)
2 suitable lengths of 3/8" OD copper tubing (F,G)
2 copper couplings 3/8" OD



The cold finger condenser is probably the most complicated part of the build. It's basically a 3/4" pipe with end caps soldered on the ends. Two holes are drilled in the side and a small length of 3/8" copper tubing is soldered in place. The length should be chosen so the condenser can slide into the top of the column and when the condenser is centered in place the 3/8" pipe protrudes a bit.

Two lengths of 3/8" copper tubing are bent and soldered from the 1/2 - 3/8 reducer on the liebig to the cold finger condenser using 3/8 copper couplers. Once the condenser is soldered into place you can solder the copper test cap at the top of the column.

Some more pics detailing the construction



From top-left going clockwise:

- The cold finger in place at the top of the column showing the short lengths of 3/8" tubing protruding.
- The cold finger soldered into place detailing the 3/8" copper couplers
- final assembly with the copper test cap soldered at the top of the column
- detail showing a notch in the short 3/8" tubing to allow water to flow easily
- using the top the column as a jig when soldering the short 3/8" tubes into place so the tubes are perfectly aligned.

Of course, the cold finger could be connected to the liebig using flexible vinyl tubes, but I wanted something 100% - mostly for looks.

Misc build items

There are some minor misc items that have to be built as well. To connect the water supply to the liebig condenser solder 2" long pieces of 1/2" copper pipe to the other half the 1/2" unions. A common garden hose has the same inside diameter as 1/2" copper pipe so simply slide on a garden hose and use a utility clamp to tighter and make water tight.



For packing I used structure copper mesh. A bought the structured mesh from a local garden supply shop. It is used as a copper fence to keep slugs out of your garden. Mostly likely an organic garden store will carry this rather then a big box Home Depot type store.



The copper mesh comes in a roll that is 5" wide. I made three rolls so the total length is 15". To keep things tidy I unraveled some of the copper mesh to create a copper thread. Using this thread I sewed the three rolls together to make one nice 15" continuos tube. Then I soldered (using the soldering iron tip) a solid copper wire to the copper mess and left 1" of wire off the end so it can be easily pulled out of the column after distilling.

With some left over mesh, roll up a small amount to fit into the output tube. This will improve the efficiency of the liebig condenser and produce a nice output stream when doing stripping runs at max heat.

A suitable cork stopper that fits the top of the output tube should be drilled so a therometer can be inserted.

[GingerBreadMan]

Setup

1) Preparing the Flour dough for sealing: The pot and the still head attached to the column are sealed with a flour dough mixture. More detailed instructions on creating this flour dough seal can be found here -

Flour dough sealing thread

I use about a 1/2 cup of flour to 1/4 water.

2) Fill the pot with 10-12L of wash. Turn on stove to max to get the wash heating started up.

3) Apply the flour dough to the rim of the cut off bowl that has been soldered to the pot.

4) Put lid on top and secure with 8 binder clips to the pot.



5) (Optional, not needed for stripping runs) Insert Copper mesh packing, leave about 1" space from the bottom.



6) Attach distillation column. Use remaining dough to seal connection between column and pot.





7) Attach water supply hoses. Now is a good time to test the water supply for leaks, etc. before the wash has heated up to boiling.



Connect thermometer probe at top of output tube.





9) Insert some rolled up mesh into the liebig condenser. This really improves the efficiency of the condenser and reduces dramatically any sputtering or 'huffing' sounds when the still is run at max.


..........

Tear down

1) Turn off stove. Turn up cooling water and open cold finger valve (if not already open). Wait for distillate to stop dripping out of liebig condenser. I also wait until the thermometer reads below 60 before starting the tear down. In other words wait a good 15 minutes for the apparatus to cool down.

2) Disconnect water supply and remove thermometer.

3) Move pot to sink. Remove Binder clips. Break seal on lid and remove lid/column from pot.



4) Using a small knife, remove flour dough paste mixture from rim of pot. Clean as good as you can.

5) Dump hot slops - careful don't burn yourself - it will still be quite hot.

6) After column/lid has cooled down - you might even want to run under cold water - break flour dough paste seal. Remove column from lid. Note: this step is a lot easier after the column lid has been cooled, if it's still hot it will be difficult to separate due to any expansion of the metal that happened when it was heated up.

7) Tear down rest of assembly, clean up with SS scrubby and put away.

[GingerBreadMan]

Sea Trials of the new still

A new still build, wouldn't be complete with first run results, so here they are.

Cleaning run

After cleaning with vinegar and water as best as I could, I decided to toss in a simple sugar wash 10% ABV and run it to dork around with the new controls. First observations were surprising somewhat.

My first thoughts about how the still would operate in reflux mode (max purity with packing and cold finger condenser on) would be to run it at low heat with a bit of cooling. This proved to be wrong. The temperature would fluctuate up and down like a wild roller-coaster ride.

Turned up the heat to 7 on the stove and cranked up the water flow and she settled down to a constant temp. I managed to get 87% ABV from the 10% wash.

Nothing scientific to report here, didn't take much notes. Ran the wash twice to clean her out for the maiden voyage.

Stripping runs - Rum

Did two stripping runs, no packing, stove at max. Each run started with 11L of about 9% ABV rum wash. From heat up to collection stop I was able to strip 11L in about 75 minutes. I stopped collecting when the output was about 30%ABV (97C on the thermometer).

Sprit run - fractionating mode

Here was the real test. Combined the two stripping runs with some left over feints from a previous rum run. Dilluted to 40%ABV with distilled water - had about 7L in the pot.

I ran this run with a setting of 4 on the stove after she came to boil. Had packing in the column but the cold finger condenser was off. Based on data on previous runs on my old still I averaged probably about 7-10% more ABV at the output. My usual expectation to collect enough to make 4 bottles of 40%ABV rum and keep the rest (head and tails) as feints for the next run.

Some raw data -

19 minutes - time to boil
... heads collection....
39 minutes - last of the heads collected and sampled 200ml of 85%ABV
... hearts collection (some heads still - but I like the taste)
111 minutes - finished collecting my spirits for bottling, last sample was 79% ABV

Basically, I was collecting 225 ml every 12 minutes or so. The ABV would drop about 1% every 225ml collection. Taste progressed from heads, to hearts as expected.


I've made this recipe several times and I'm familiar with the taste. I really liked what was coming off the still flavor wise. I hit my goal of collecting enough to dillute down to 40% ABV and make 4 750ml bottles.

Normally, with the old pot still I would be just hitting the tails (well my taste of it) at about 65% ABV at this point. I think I could have made an extra bottle out of the deal, but didn't want to get greedy. Will let you know in a couple of days how it really tasted.

Reflux - with cold finger

Have limited data to report here. I'm still figuring out how to run the still in reflux mode. After the 120 minute mark of doing the sprit run above, I decided to dork around some more. Insulated the column and turned on the cold finger. Tried running at lower stove temp to have it somewhat equalize. The temps went up and down like see saw.

I then turned the stove up to 6 and turned up the water flow. I felt kinda bad just running all this good water down the drain (rate was 3L/minute). I'll have to get a pump to conserve water at this rate.

Temperature settled down to 79C. Collected 250ml and it was 90%ABV.


I don't have any experience with reflux still. This one is different, since it doesn't have a method of creating equlibrium. Also it's a pretty short column. I'm pleased with the 87-90% purity I can get from it. I have 20L of vodka wash to try next.

Perhaps someone with more experience and insight could shed some light why it runs stable at a higher stove setting with more water flow, then at a lower stove setting with the normal water flow I use during stripping and spirit runs.

-------------

That's all, hopefully this information was useful, even if you don't intend on building this kind of still.

[Tater]

Part of problem is probably the way your heating. Elect stoves switches cycle power on and of at different periods of time to get heat wanted .Hi power on all time medium power on 50 percent of the timed cycle. There called infinite switches. Like your work very nice setup Ill put a sticky on it .

[HookLine]

This is one of the best, and best documented experiments I have seen here. Full marks, including for the thoughtful, original and compact design.

As it is, it isn't quite a fully controllable reflux still, so I don't think you are going to be able to get all the way to 95%. If you put a gate valve between the column and the Liebig condenser to control vapour flow into the Liebig you would have a VM still, and you might be able to get close to 95%, but it would depend a lot on how much reflux that cold finger could generate. You would also have to put a safety vent somewhere before the valve though.

Basically, I was collecting 225 ml every 12 minutes or so. The ABV would drop about 1% every 225ml collection. Taste progressed from heads, to hearts as expected.

Try running a bit slower, maybe 150 ml every 1/4 hour, and see what happens.

And what tater said about the cyclical heating of stove top elements.

[GingerBreadMan]

tater - Well that makes perfect sense, the stove cycling on and off producing the wild temperature fluctuations. Looks like I'll have to either get a pump to conserve water and run it high or look into a heating control that doesn't cycle.

hookline - thanks, this post (or posts) where created over the period of 3 weeks. I built the posts at my own discussion board editing/adding a bit at a time. I learned so much reading so many posts, that when I wanted to post about this still I thought it would be handy to put as much information as possible in one continuos post here. My expectation for running as reflux still was about 90% purity, so I'm quite pleased with the outcome. I believe I can make good enough vodka for coolers by first doing a stripping run, not going into the tails and then doing a reflux run at 90%. It might be wasteful tossing the tails but white sugar is so cheap compared to buying vodka or coolers at the store.

[Tater]

Most of the big eyes on stoves are 2400 to 2700 watts.Small ones 1500 to 1700 So small one on high is is little over half the temp.You could all ways get a single burner hot plate and make /get a controller for it.

[Loki440]

Glad you posted this, as ive been lurking heavily for the last week gulping up information like a fish in water, but i was thinking along the same lines, just couldn't formulate exactly what i wanted, but with this i finally settled on a design as my application is more or less the same.

But gonna change a couple things up vs your design that i believe will have an improvement.

[CoopsOz]

Really nice work GBM, I think I can speak for all when I say I appreciate the effort.

[GingerBreadMan]

I have some data on my first vodka run. I wanted something neutral for vodka coolers - and just in time there's a bbq this saturday and we'll be bringing over a batch of them.

I started with 30L of wash - 10L of bird watchers, 10L of vodka made by adding sugar and water to the lees of wine, and 10L of turbo. Stripped them all to about 40% ABV and stopped collecting. Probably wasteful, but I wanted something clean and white sugar is so darn cheap anyways. Taste wise after stripping I really liked the one made with wine - but then again I'm a wine drinker.

I added all three stripped runs to a small carboy, added about 5 tsp of baking soda and let it sit for a week. Shaking it once in awhile. I filled up my boiler - maybe 7L? Darn I wish I measured the ABV and the amount - I was just so excited about doing a vodka run - the still running in forced reflux with packing.

As the temps came up, I turned the stove down to 5, turned up the water. Very wasteful letting all that water go down the drain, I'll probably get a pump to recirculate it next time.

Temps came and held steady at 78. I was surprised the first 300ml had a heads taste to it. But then came some nice neutral stuff and starting collecting it. I collected at a rate of 16ml/minute. It held steady at 91%ABV for 1.8L. Then it started to slow down to dripping, taste changed a bit. When it was just a drop a second or two, I decreased the water flow to the condenser. It picked up but the ABV dropped quickly to 85%ABV then 80%ABV. I figured it was done. So I shut her down.

Eager to try it out, I dilluted the hearts I collected to 40%ABV. Nice stuff. I am quite pleased.

Don't know much about forced reflux column stills, but from what I read it behaved very much like a VM still - running a steady temp/flow rate until it started to really slow down.

I'm letting the backset cool down to take an ABV of what was left in the pot. Will post that tomorrow.

Just going to have a few quick shots to sample

Edit: Well the backset cooled faster then I thought it would. ABV left in the pot was 12%ABV (temperature corrected). Hmm... maybe a bit wasteful, but white sugar is cheap

[HookLine]

Sounds like a success to me!

The only suggestion I have is to try running it slower, about 8-10 ml a minute. My bet is that will up the quality a fair bit.

[GingerBreadMan]

I think to run it at a slower rate I need to solve the stove cycling problem. At lower settings on the stove the temp goes up and down like a roller coaster. At a setting of 5 it will be steady. The condensor at the top is not the most efficient - small cold finger so to get the collection rate down I would really have to increase the water flow to an unbelievable level.

Still some bugs to work out in vodka mode. I have ideas, hopefully they are not too crazy. I'm leaning to making that double boiler I always wanted for the fruit washes I want to do next. I'm thinking a double boiler will solve the fluctuating temp swings when the stove in on low - the water in the double boiler would act as a buffer.

hmmm.... on my second shot, I'm still pleased.

[HookLine]

Ahh, yes, the cycling stove element problem, I remember now.

A double boiler might solve that problem, but it might not too.

One possibility to improve the reflux condenser is to solder some vertical copper fins onto the cold finger to significantly increase the cooling surface area. Or maybe just wrap it copper mesh.

[new_moonshiner]

that was gonna be my question how efficient is the cold finger condenser ? I like the small compact design ,Just the lack of surface area as hook pointed out would be my only real concern ..

[new_moonshiner]

that was gonna be my question how efficient is the cold finger condenser ? I like the small compact design ,Just the lack of surface area as hook pointed out would be my only real concern ..EXCELLENT job by the way .

[GingerBreadMan]

It's totally inefficient. If I were to design it again, I would add another 4 inches to the cold finger condenser. Maybe put a scrubby up there.

Right now I run the cooling water pretty fast. Don't pay for water, it's included in the rent. I feel wasteful with all that water going down the drain.

I still can knock down all the vapors if I turn the tap up to full, as it is.

--------

Most of the time I'm running her without the cold finger on at it all. Either stripping (without packing) or with 15" of packing with the stove at about 4-5 make for a nice fractionating still. I only use the cold finger for vodka, or just recently I wanted to do a single run 150 proof. The wash was 8%-10% ABV and I could get 150 proof steady out of her with the cold finger on.

[GingerBreadMan]

I should add, I designed this still to fit the space requirements I had. The pot fits nicely in the cupboard in the kitchen. The rest of my distilling equipment fits nicely in this drawer -



Some day, we'll have a house with acreage. Right now we are in a 2 bedroom apartment saving our nickels and dimes for that house - with room for serious distilling!

Hence the need for a small compact, yet inefficient cold finger condenser at the top of the column

[tripnoncid]

How much did all of this cost?
thanks
trip

[GingerBreadMan]

Don't know. Already had the pot and had some copper left over from a previous still project. I would guess $150, maybe.

[thenewestnoise]

Hi, first post ever!
Anyway, do you think that the cycling element problem could be solved with some sort of heat sink, like a big piece of steel which you could put on the burner and then put your still on top of? It would take a long time to heat up, of course, but would minimize changes in temperature due to cycling. just a thought...

[rad14701]

Hi, first post ever!
Anyway, do you think that the cycling element problem could be solved with some sort of heat sink, like a big piece of steel which you could put on the burner and then put your still on top of? It would take a long time to heat up, of course, but would minimize changes in temperature due to cycling. just a thought...

Welcome to the forums, thenewestnoise... Yes, this concept has been covered elsewhere in the forums several times... I use a steel plate with my stove top still to equalize the heat fluctuations caused by cycling...

[pHneutral]

I think an old disc brake would work for this, FYI. a lot cheaper than buying an actual steel plate

[rad14701]

I think an old disc brake would work for this, FYI. a lot cheaper than buying an actual steel plate

A finned brake rotor might tend to dissipate too much of the heat input, however... I can usually lay my hands on plenty of scrap plate for free - usually in the same heap of scrap as the brake rotors... Sure helps to come from a family of hoarders...

[Ugly]

One of the problems with running an electric stove element for a long period of time is the amount of heat that is reflected back to the area where the element connects. Consider that they are designed for cooking dinner with the biggest job to make the odd pot of soup. If you suddely stick a big steel plate on one, you reflect enough heat back into the connections to damage even the high temp insulation on the wiring.

How do I know? I tried it the first year I made maple syrup and literally melted the wiring right out of the element junction. Once I took it apart, the connections on the other elements also showed signs of decay as we often leave large pots of hot water on the stove for making candles and soaps, not unusual for the stove to be on 10 hours a stretch. I changed all the wiring and connections with a high heat silicone insulated wire used for commercial applications in hot areas. I also increased the gauge of the wire to help things out. I've only lost one terminal end since I did that. Older stoves often use aluminum wiring which can be another weak point.

Your results might vary, I'm just sharing what when on with my trials

[rad14701]

You make a valid point there, Ugly... I've had to make sure that heat wasn't being reflected back down into the stove as well... A sure sign that too much heat is reflecting back is darkening of the insert under the electric element itself... I noticed mine showing initial signs of darkening and checked to find that the entire stove top was getting warmer than I liked... The plate I use now actually raises the pot up higher and alleviates the heat buildup... My plate is only as big as the element itself with no overhang so air circulation is now better than with no plate at all...

[fred45]

Hi, I have never disdilled liquor but I have been a professional cook. the heat variation problem can be solved by putting a thick wire mesh on the burner under the pot, like "hog wire" fencing. there are also spacers that have ceramic beads on them to reduce the heat to the pot. with the space you can run the stove hotter but have a cooler pot temp. you will have to try a couple thicknesses to get the right space but then you can run you pot slower

[cousingary]

I probably missed this but; how do you attach the column to the stainless bowl? Is it possible to solder or braze stainless to a copper fitting? Should I find a stainless pipe fitting and weld it to the bowl? What type of welding/soldering/brazing is needed (rod, wire, flux, gas)? Thank you for this excellent thread;

Gary D

[rad14701]

I probably missed this but; how do you attach the column to the stainless bowl? Is it possible to solder or braze stainless to a copper fitting? Should I find a stainless pipe fitting and weld it to the bowl? What type of welding/soldering/brazing is needed (rod, wire, flux, gas)? Thank you for this excellent thread;

The soldering issue was covered in another topic just today... Yes, you can solder stainless to copper...

I use a SS kitchen sink drain between the SS bowl and the column... I could have just as easily soldered a copper fitting onto the bowl...

[cousingary]

OK, thanks rad; I looked at your rig...extremely clean...great idea. Finally got a ss strainer today. How did you solder the nut to the pipe? Can't find a brass nut and the one that came with the strainer looks like pot metal or fake chinese brass (zinc over steel?) which I haven't tried to solder before.
Gary