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                                                                      Exhibit 13


                                  AMENDMENT TO
                          SHAREHOLDER RIGHTS AGREEMENT


        Amendment, dated as of October 20, 1999 (the "Amendment") to the
Shareholder Rights Agreement, dated as of August 3, 1994 (the "Rights
Agreement"), by and between Ferrofluidics Corporation, a Massachusetts
corporation (the "Company"), and American Stock Transfer and Trust Company, a
New York corporation (the "Rights Agent").

                               W I T N E S S E T H

        WHEREAS, Section 27 of the Rights Agreement provides that prior to the
Distribution Date (as defined therein), the Company and the Rights Agent shall,
if the Company so directs, supplement or amend any provision of the Rights
Agreement as the Company may deem necessary or desirable without the approval of
any holders of certificates representing shares of the Company's common stock,
par value $.004 per share (the "Common Stock");

        WHEREAS, the Company intends to enter into an Agreement and Plan of
Merger (the "Merger Agreement") with Ferrotec Corporation, a Delaware
corporation ("Parent"), and Ferrotec Acquisition, Inc., a wholly-owned
subsidiary of Parent ("Sub"), pursuant to which Sub will be merged with and into
the Company upon the terms and subject to the conditions set forth in the Merger
Agreement (the "Merger"); and

        WHEREAS, prior to entering into the Merger Agreement, the Company
desires to amend certain provisions of the Rights Agreement.

        NOW, THEREFORE, in consideration of the premises and the mutual
agreements herein set forth, the parties hereby agree as follows:

        1. Section 1(a) of the Rights Agreement is amended by adding at the end
of Section 1(a) a new paragraph which provides as follows:

        "Notwithstanding anything in this Agreement to the contrary, neither
Ferrotec Corporation ("Parent"), Ferrotec Acquisition, Inc., a wholly-owned
subsidiary of Parent ("Sub"), nor any of their Affiliates or Associates shall be
deemed to be an Acquiring Person, and no Stock Acquisition Date, Distribution
Date, Section 11(a)(ii) Event or Section 13 Event shall occur, as a result of
(i) the execution and delivery of any Agreement and Plan of Merger by and among
Parent, Sub and the Company (the "Merger Agreement"); (ii) any action taken by
Parent, Sub or any of their Affiliates or Associates in accordance with the
provisions of the Merger Agreement; or (iii) the consummation of the Merger (as
such term is defined in the Merger Agreement) in accordance with the provisions
of the Merger Agreement. In addition, notwithstanding the foregoing, a Person
shall not be an "Acquiring Person" if the Board of Directors of the Company
determines that a Person who would otherwise be an "Acquiring Person," as
defined pursuant to the foregoing provisions of this Section 1(a), has become
such inadvertently, and such Person divests as promptly as practicable (or
within such period of
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time as the Board of Directors determines is reasonable) a sufficient number of
shares of Common Stock so that such Person would no longer be an "Acquiring
Person," as defined pursuant to the foregoing provisions of this Section 1(a).
Notwithstanding the foregoing, upon the termination of the Merger Agreement in
accordance with its terms, this paragraph shall become null and void and of no
further force or effect."

        2. At the Effective Time (as defined in the Merger), the Rights
Agreement and the Rights shall terminate and become null and void and of no
further force or effect.

        3. Any term used herein and not defined shall have the meaning ascribed
to such term in the Rights Agreement.


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        IN WITNESS WHEREOF, the parties hereto have caused this Amendment to be
duly executed as of the day and year first above written. This Amendment may be
executed in one or more counterparts all of which shall be considered one and
the same amendment and each of which shall be deemed to be an original.


ATTEST:                                     FERROFLUIDICS CORPORATION



By: /s/ Jean A. Scische                     By: /s/ William B. Ford
   ------------------------------              ---------------------------------
   Name: Jean A. Scische                       Name: William B. Ford
                                               Title: Vice President


ATTEST:                                     AMERICAN TRANSFER AND TRUST
                                            COMPANY, as Rights Agent



By: /s/ Susan Sidler                        By: /s/ Herbert J. Lemmer
   ------------------------------              ---------------------------------
  Name: Susan Sidler                           Name: Herbert J. Lemmer
                                               Title: Vice President