Here is the answer to your question.
I'm interpreting your question to mean that you have a small piece of Sterling Silver which has detached or broken off of your Sterling Silver teapot.
To reattach the small piece to the teapot, here is what you will need -
1. A small, adjustable, preferably hand-held butane torch (or something equivalent). You will need a flame torch because a soldering iron generally won't be able to deliver sufficient heat to the work piece to produce reliable solder joints. A butane torch is best, XXXXX XXXXX produces a clean flame which will minimise blackening of the solder joint.
Most hardware stores stock a variety of portable gas torches for hobby use. They are often labelled "Micro Torches" because they are so small. Any of these would be ideal for your purposes.
2. Sterling Silver Solder. This comes in several grades, called Hard, Medium, Easy and SuperEasy - which refers to the temperature at which the solder melts or begins to "flow". Here are the typical "flow" temperatures for the different grades of Sterling Silver Solder -
- Hard (1450 °F / 788 °C)
- Medium (1360 °F / 738 °C)
- Easy (1325 °F / 719 °C)
- SuperEasy (1207 °F / 653 °C)
The higher temperature solder will produce a stonger bond between the two surfaces being joined, because the solder joint will penetrate deeper into each of the joined surfaces. If the strength of the joint is not critical, then a lower "flow" temperature solder can be used.
Sterling Silver solder is commonly available in three forms - Sheet, Wire and Paste. The wire or paste is probably most suitable for small domestic repair jobs. The paste, which is normally supplied in a syringe, is particularly convenient to use because it can be applied exactly where it is required on the surfaces to be repaired, before the repair is commenced.
Sterling Silver solder in its various forms can be obtained at most jeweller supplies or hobby shops. It is expensive, but you won't need very much to do your teapot repair job.
3. Flux. The flux is either a liquid or a paste which is applied to the two surfaces to be joined prior to the application of heat and solder. This helps to remove any contamination from the area and ensure good adhesion and bonding between the solder and the repair surfaces. Most Sterling Silver solder pastes include a flux in their composition, which further adds to their convenience.
4. A Heat-Proof Work Surface. When using soldering tools, the work should be done on a surface that won't be damaged by molten solder, hot pieces of metal or misdirected butane torches. A heat-proof work area - even something as simple as a large wooden board mounted on rubber feet - is essential for safe conduct of Sterling Silver repairs.
An additional consideration here is that the chosen work area should be well ventilated. This applies naturally for activities which involve the use of an open flame, but are also important because the soldering flux and pickling solutions can give off unhealthy fumes.
5. Various Tools. For example, large insulated tweezers, needle-nose pliers and similar will be needed to hold the repair parts in place while applying heat and solder to the repair. You might also need some steel wool if a rough solder joint needs to be cleaned up a little after it has been allowed to completely cool down.
6. Pickling Solution. After the repair is complete and the item has cooled down sufficiently to be handled again, it should be cleaned with a "pickling solution" to remove any residues, blackening and scale from the soldering process. An acid (typically hydrochloric acid) is often used for this cleaning process, and might be dabbed onto a small repair using cotton buds or similar. However, safer pickling "gels" or "pastes" might be available from hobby or jeweller supplies.
Once the repair has been sufficiently "pickled" to remove any residues and blemishes from the soldering process, it should be thoroughly washed and dried to ensure no trace of the pickling solution remains, in readiness for polishing.
7. Polish. The repair should be polished once the pickling process is complete. Any commercially available Sterling Silver polish will be suitable for polishing the repair site. The polish should be applied with a soft material such as cotton wool, rubbed, rinsed and buffed to bring out the Sterling Silver shine.
NOW, how to go about actually DOING the repair?
The basic process of soldering two metal parts together (for example, a teapot and a broken piece off the teapot) is as follows -
1. If a separate flux compound is being used, apply that to both of the surfaces which are to be joined. The flux should be "painted" onto each of the two surfaces to be joined, sufficient to just cover each, with no excess.
2. If a solder paste is being used, apply it to just the main piece of the two items to be joined. Again, "paint" sufficient of the paste to cover the actual area of the intended solder joint, with no excess.
3. Position the teapot so that it won't be able to move, with the area that you are working on easily accessible with your torch and tweezers.
4. Light up your torch and adjust it's flame to be able to apply heat to your solder area without risk of the force of the flame "blowing" solder off the joint area.
5. Apply the torch to the repair site on the teapot, while at the same time holding some solder wire with a pair of tweezers against the repair site, until the solder begins to melt and "flows" onto the repair area (or, if solder paste is being used, until the solder paste begins to melt and "flows" across the repair area). You may need to keep adding solder wire a little at a time, while keeping the flame applied, until the entire repair area has been "wetted" by molten solder. The process will be easier if solder paste has been used.
6. When the entire repair area (the area of the intended solder joint) has been "wetted" with molten solder on the teapot, then (while keeping the repair area hot with the flame) with a pair of tweezers or pliers, bring the piece which is to be joined to the teapot into contact with the joint and hold it in the position that it is intended to have until you can see that it has also been fully "wetted" by the molten solder.
7. You should now remove the flame from the repair area and allow the solder joint to cool down and solidify. It is very important that the part which is being joined to the teapot is held very still and not allowed to move as the solder joint solidifies. It might take 10 seconds or longer for the solder joint to solidify, so you should be careful to hold the pieces very still until certain that the joint is solid.
8. If the joint doesn't turn out to your satisfaction, then you can apply the flame to remelt the solder and adjust the parts' positioning, or even separate the two parts completely and rejoin them. Then the part must be held in place again until the joint solidifies.
9. Once the joint has solidified and you are happy with your handiwork, you should allow the teapot to cool down completely. Then you should pickle and polish the repair as described above.
10. It might be helpful, before undertaking the repair of the teapot, to obtain a couple of small pieces of expendable Sterling Silver, and experiment with soldering them together and separating them again, until you are comfortable with the process. The soldering process is very much a learnt skill, and it becomes easier with practice.
Please let me know if you need further assistance with this answer.
I hope this helps.