Talmud for Rosh Hashanah 53:10
ובתעניות בשל זכרים כפופין ופיו מצופה כסף: מאי שנא התם דזהב ומ"ש הכא דכסף איבעית אימא כל כינופיא דכסף הוא דכתיב (במדבר י, ב) עשה לך שתי חצוצרות כסף ואיבעית אימא התורה חסה על ממונן של ישראל
Why then is the blast of the shofar prolonged? - So that people should know that the proper ceremony of the day is with the shofar. ON FAST DAYS THEY USED CURVED SHOFARS OF RAMS' HORNS THE MOUTHS OF WHICH WERE OVERLAID WITH SILVER'Why in the other case should gold have been used and here silver? - If you like I can reply that for all public gatherings silver is used, as it is written, Make thee two trumpets of silver,<span class="x" onmousemove="('comment',' Num. X, 2. V. supra.');"><sup>17</sup></span> or if you like I can say that the Torah wished to spare Israel unnecessary expense.<span class="x" onmousemove="('comment',' Lit., 'had mercy on the money of Israel'.');"><sup>18</sup></span>