I have a Yamaha G2 which has always sounded brash/hard/bright to me. I spoke to my piano technician about it and he changed the tone dramatically. It is now much warmer. He did it, at least in part, by placing each hammer for a short time in the steam coming from a tea kettle. Not being a technician myself, is this technique common?

It is becoming more common all the time. Roger Jolly and David Stanwood were among the earliest, (to my knowledge), techs to promote this approach.
Many of the Asian hammers made from the early 1970's- 2000 are extremely hard, compressed rocks. Needles have to tear too much fiber to get any resilience, so steam allows the outer layers to relax as a unit. Some techs like to just steam the very crown, others prefer to loosen the shoulders first. I use a 1" strip of wet flannel, squeezed out as dry as my hand can squeeze. A fast pass with a hot iron when the strip is laid down the row of hammers will make a dramatic difference, instantly. Is easy to overdo it, and then the hammer balloons out. If that happens, you need new hammers.
Regards,

Ed,

I've used steam with various contrivances to good effect. I've mostly used it on cool pressed hammers like Ronsons where the belly was new and very responsive. I found the effect to be short lived, at least on the cool pressed hammers.

Do you find that the hot pressed rocks hold the effect longer?

Jim Ialeggio

I think there was a bit of a wave of steam voicing, I know a lot of techs who once did it use it much less today.

I went through my steaming phase about 10 years ago. I hardly ever use it now. Steam often warms up the tone but the cost is articulation. It also can be unpredictable. On some hammers it will cause the crown to pinch together and narrow. I see it as a "quick and dirty" voicing method that may have its place on some cheap pianos. Proceed with much caution on nicer instruments.

There are some hammers I would not use steam on. In particular, all these sets of Renner Blues that I have scattered around town over the last decade or so. The normally impregnated Steinway hammer reacts poorly to this approach, also. However, the hard rock hammers I have seen on many imports react well, and saves me hours of turning the hammers to dust with my needles.
I loosen the shoulders, on both sides, first. Then, usually, a very light pass over the strike points. After this, I can usually get the needles in deep enough to take some of the granite out of the lower levels of felt. I don't think the effect of steam can be gotten to the inner parts of the hammer without causing the whole structure to let go. I see it as a way of relaxing the entire outer shell, and yes, sometimes the tops have to be filed.
There is also the occasional last ditch use, ie, a donated 1980's era U1 to a jazz school was so bright it sounded like metal. No budget for flat spots and string cuts. 15 minutes later, the piano had a big, round, warm sound. A year later and it is still much improved and in heavy use. That is "shade tree" piano technology, but it is also real value for the money.

For voicing, I prefer accupuncture, never use the vise grips, often dose with the acetone/lacquer combo, but sometimes when the time/felt/money/customer equation lines up a particular way, steaming the hammers is the clear route to a satisfied customer, (which is what I have always looked for).
Regards,

Thanks very much.