The Sofer
The scribe who handwrites the scrolls for the tefillin is called the sofer. He undergoes rigorous training and and an apprenticeship with an expert to acquire  the necessary skills. In addition to intimate knowledge of the materials and technique, he must be a G‑d fearing Jew who understands the magnitude of the task he faces daily.

The Sofer's Quill
The sofer uses a turkey feather or reed as a quill, called a kulmus in Hebrew. The feather is used by Ashkenazi scribes, while the reed is commonly used by Sephardim. A sofer endeavors to use a nice-looking kulmus as this is an expression of endearment for the holy task. The making of the kulmus is of great importance. It is an acquired skill to create a perfect quill that will create sharp, fine lines, bold, flat strokes and clean, rounded corners. The success of a sofer is partially dependant on being able to make a proper quill. An expert sofer will know how to press the quill onto the parchment with limited pressure. This will enable the sofer to use the quill longer without the need of a trim.

Sofer's Ink
The Hebrew term for ink is diyoh. Unlike in yesteryear when each sofer produced his own ink, and the quality varied accordingly, today the sofer purchases ink at a store that carries safrut (scribal) supplies. There are perhaps a dozen ink makers. The sofer chooses his ink of preference.

In the winter the ink sometimes becomes runny, so the scribe might leave the cap off to let it thicken a bit, while in the summer he may add water or other chemicals, as directed by the ink maker, to thin the ink. Over-watering will make the ink grayish and may affect the halachic status of the writing and will surely cause the ink to fade more quickly to an unacceptable shade, so proper care of the ink and maintaining the fine balance is critical.

The ink is made of Gum Arabic, which serves as the bonding agent, tannic acid from the gallnut and ferrous sulfate or copper sulfate. These two chemicals cause the ink to turn black. According to Halachah, in order for the ink to be kosher it must be pitch black. Over the years the ink on the parchment may turn a reddish or rusty color from the copper sulfate. This natural process takes many years, and many halachic authorities consider the tefillin kosher even if the letters have reddened, if it has been over a long period of time.