Urethane and Polyurethanes

I have to admit...

David Weaver

...it makes for gorgeous looking cherry and mahogany, but my threats to my health will have to end at lack of exercise and appreciation of junk food.

Carcinogenic stuff like that is beyond me.

Glad I don't work in a lab and have to make a judgement call about stuff like this - from the videos of it, it appears to really do a superb job cleaning glass.

Bill has posted before that many of the old recipes for stains and various things with woodworking are half necessary and half BS where additional ingredients added by guessing have no beneficial effect, and sometimes are counter to the goal, on top of being highly toxic.

I don't even like thinking about sucking in the fumes from water base crosslinked finish (I spray with a mask, but once in a while run in and out of the shop while I'm waiting for the dust to settle) - who really knows what the effects are?

cement rash

Bill Tindall, E.Tn.

You can be sure it is NOT in cement. I don't know what cement rash is but if you get wet Portland cement on your skin it will dissolve. It contains calcium hydroxide and other bases and has a pH of 13 thereabouts. Might as well stick you arm in a solution of lye.

some chemistry

Bill Tindall, E.Tn.

It is a powerful oxidizing agent. Dissolved in concentrated sulfuric acid it is even more so. So if one, in the day, wanted clean glass a quick swim in a vat of chromate in sulfuric acid did the trick. But this was a piddly market.

It is an exceptional passifier for corrosion mitigation on steel. It was added to brine systems by the ton and formulated in steel primers. And it was used in tanning leather.

While it is feared that walking by it may cause harm, inhaling it is the hazard that is well documented. I have shown that it persists on wood after application. I actually thought the lignin would destroy it but it didn't. Next step is sanding and you see where this is going............

Young and dumb!

Jim Dillon

Bill, thanks for memories. During my chemistry

"intern" years, I remember vats of concentrated sulfuric acid/potassium dichromate along-side vats of sodium hydroxide solution both used to clean out carbonaceous polymers from glassware. And tons of acetone to wash the clean glassware. Ah, those were the days! Lab safety (?). Instructions said to make sure one wore rubber gloves before dipping your hands into the vats! Dah!!! Not so young and but still dumb, Part II. Flash forward to my first real job synthesizing a biodegradable polymer made from propiolactone. Splashed that stuff everywhere! Only later did I find out it (the monomer) was a suspected carcinogen.

Hey, live and learn/survive. So far, so good, but knock-on-wood.

I agree with you regarding the usage of potassium dichromate for furniture. With so many other viable options available, I would avoid it.

Jim

not knowing anything ...

David Weaver

..about chemistry, and possibly misreading things, it appears that chromium is either in cement naturally or on purpose and at some point in manufacture or cure, some of it becomes hexavalent chromium.

the NIH has a bunch of studies where they found cement/concrete workers were sensitized to potassium dichromate.

https://journals.lww.com/dermatitis/Citation/2008/07000/Potassium_Dichromate.57.aspx

When I read about potassium dichromate initially, some of the references made it sound like "as an additive, it's used to slow the cure of cement", which would lead one to believe that cement should be orange. it sounds more like it's just there.

https://www.osha.gov/dsg/guidance/cement-guidance.html

(there's a reference at the bottom of this article about the origin of the chromium in the cement and possible ways to lower it).

As you mentioned that it's really breathing it that's the problem (and sanding off old finish was the first thing that came to mind - someone may sand those pieces in the future and suck it right in), maybe it's less of an immediate issue with cement because most exposure is to wet cement.

Interesting topic - I learned something from it, still point being that shellac is still a common finish in high end work. My separate experience is that if the person making the furniture is around, it's a very suitable top coat for most furniture items. repair of kid slobber marks and wet rings from sweating glasses was extremely quick. I certainly didn't use it for my kitchen cabinets, though - except to tone the wood under the top coat (crosslinked target 6000 series stuff).

Re: cement rash

John in NM

Only trouble I ever had with portland cement is a bit of dry skin. Annoying but not enough to worry about much. I've made lime plaster with type S lime (slaked) and never had trouble with that either though I recall it dries skin a bit more than portland (dry being a bit of a misnomer, it removes oils from skin, leaving it feeling flaky, dry, and easily cracked).

Quick lime (un-slaked) is what I always heard was the bad one that seriously damages skin. Never used any though, its a bit hard to find in any case and the type S works so well that there is no point to looking - at least when making plasters.

the source of Cr(VI)

Bill Tindall, E.Tn.

Apparently the chromate comes from slag which comes from iron ore processing. It must be that iron ore that contains chromium forms it in the refining process. As I recall iron oxide ore is heated with limestone and coke. Chromium of some lower valance state must extract into the calcium oxide formed in the slag and at these temperatures becomes oxidized to Cr(VI). Seems backward to me in that the refining process is reducing and Cr(VI) will only form in a highly oxidizing environment. There is obviously some detail of the process I don't understand. In any case the amount is tiny. I never heard of it. Given that only some ore will contain chromium I wonder how wide spread the occurrence is.

rest of the chemistry story

Bill Tindall, E.Tn.

Iron ore that contains chromium oxide (CrIII) is smelted with a mix of carbon and limestone at very high temperature. Calcium silicate and calcium oxide are formed and float to the top of the iron melt.

Chromium prefers to be extracted into the slag. Under these basic conditions (both calcium salts are highly basic), and exposure to oxygen (the top of the melt will be exposed to air) the chromium will oxidize to Cr(VI) to form calcium chromate. (dichromate is formed by acidifying any chromate solution, but both are Cr(VI) )

I can't imagine any slag contains much chromate or it would be recovered from the slag to produce chromium metal.

The amount of exposure...

David Weaver

..must not be that bad compared to people who worked in the plating industries.

But it was interesting to note that one of the ways that they found out that there was a material amount in it was sensitivity tests for cement workers showing reactions to hexavalent chromium. I have no clue what the difference is between sensitization and significant increases in morbidity or mortality. Could be a very large gap.