Exhibit 4.1



                            SUPPLEMENTAL INDENTURE

         SUPPLEMENTAL INDENTURE (this "Supplemental Indenture"), dated as of
April 2, 2004 among ISP Microcaps (U.S.) LLC (the "Guaranteeing Subsidiary"), a
subsidiary of ISP Chemco Inc. (or its permitted successor), a Delaware
corporation (the "Company"), the Company, ISP Chemicals Inc., ISP Minerals Inc.,
ISP Technologies Inc. (collectively with the Company, the "Issuers"), the other
Guarantors (as defined in the Indenture referred to herein) and Wilmington Trust
Company, as trustee under the indenture referred to below (the "Trustee").

                              W I T N E S S E T H

         WHEREAS, the Issuers have heretofore executed and delivered to the
Trustee an indenture (the "Indenture"), dated as of June 27, 2001 providing for
the issuance of 10 1/4% Senior Subordinated Notes due 2011 (the "Notes");

         WHEREAS, the Indenture provides that under certain circumstances the
Guaranteeing Subsidiary shall execute and deliver to the Trustee a supplemental
indenture pursuant to which the Guaranteeing Subsidiary shall unconditionally
guarantee all of the Issuers' Obligations under the Notes and the Indenture on
the terms and conditions set forth herein (the "Note Guarantee"); and

         WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee is
authorized to execute and deliver this Supplemental Indenture.

         NOW THEREFORE, in consideration of the foregoing and for other good and
valuable consideration, the receipt of which is hereby acknowledged, the
Guaranteeing Subsidiary and the Trustee mutually covenant and agree for the
equal and ratable benefit of the Holders of the Notes as follows:

     1.       CAPITALIZED TERMS. Capitalized terms used herein without
definition shall have the meanings assigned to them in the Indenture.

     2.       AGREEMENT TO GUARANTEE. The Guaranteeing Subsidiary hereby agrees
 as follows:

         (a)   Along with all Guarantors named in the Indenture, to jointly and
     severally Guarantee to each Holder of a Note authenticated and delivered
     by the Trustee and to the Trustee and its successors and assigns, the Notes
     or the obligations of the Issuers hereunder or thereunder, that:

              (i) the principal of and interest on the Notes will be promptly
         paid in full when due, whether at maturity, by acceleration, redemption
         or otherwise, and interest on the overdue principal of and interest on
         the Notes, if any, if lawful, and all other obligations of the Issuers
         to the Holders or the Trustee hereunder or thereunder will be promptly
         paid in full or performed, all in accordance with the terms hereof and
         thereof; and

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              (ii)     in case of any extension of time of payment or renewal of
         any Notes or any of such other obligations, that same will be promptly
         paid in full when due or performed in accordance with the terms of the
         extension or renewal, whether at stated maturity, by acceleration or
         otherwise. Failing payment when due of any amount so guaranteed or any
         performance so guaranteed for whatever reason, the Guarantors shall be
         jointly and severally obligated to pay the same immediately.

         (b)   The obligations hereunder shall be unconditional, irrespective of
      the validity, regularity or enforceability of the Notes or the Indenture,
      the absence of any action to enforce the same, any waiver or consent by
      any Holder of the Notes with respect to any provisions hereof or thereof,
      the recovery of any judgment against the Issuers, any action to enforce
      the same or any other circumstance which might otherwise constitute a
      legal or equitable discharge or defense of a guarantor.

         (c)   The following is hereby waived: diligence presentment, demand of
      payment, filing of claims with a court in the event of insolvency or
      bankruptcy of any Issuer, any right to require a proceeding first against
      an Issuer, protest, notice and all demands whatsoever.

         (d)   This Note Guarantee shall not be discharged except by complete
      performance of the obligations contained in the Notes and the Indenture,
      and the Guaranteeing Subsidiary accepts all obligations of a Guarantor
      under the Indenture.

         (e)   If any Holder or the Trustee is required by any court or
      otherwise to return to the Issuers, the Guarantors, or any Custodian,
      Trustee, liquidator or other similar official acting in relation to either
      the Issuers or the Guarantors, any amount paid by either to the Trustee or
      such Holder, this Note Guarantee, to the extent theretofore discharged,
      shall be reinstated in full force and effect.

         (f)   The Guaranteeing Subsidiary shall not be entitled to any right
      of subrogation in relation to the Holders in respect of any obligations
      guaranteed hereby until payment in full of all obligations guaranteed
      hereby.

         (g)   As between the Guarantors, on the one hand, and the Holders and
      the Trustee, on the other hand, (x) the maturity of the obligations
      guaranteed hereby may be accelerated as provided in Article 6 of the
      Indenture for the purposes of this Note Guarantee, notwithstanding any
      stay, injunction or other prohibition preventing such acceleration in
      respect of the obligations guaranteed hereby, and (y) in the event of
      any declaration of acceleration of such obligations as provided in
      Article 6 of the Indenture, such obligations (whether or not due and
      payable) shall forthwith become due and payable by the Guarantors for
      the purpose of this Note Guarantee.

         (h)   The Guarantors shall have the right to seek contribution from any
      non-paying Guarantor so long as the exercise of such right does not
      impair the rights of the Holders under the Guarantee.

         (i)   Pursuant to Section 10.02 of the Indenture, after giving effect
      to any maximum amount and any other contingent and fixed liabilities that
      are relevant under

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       any applicable Bankruptcy or fraudulent conveyance
       laws, and after giving effect to any collections from, rights to receive
       contribution from or payments made by or on behalf of any other
       Guarantor in respect of the obligations of such other Guarantor under
       Article 10 of the Indenture, this new Note Guarantee shall be limited
       to the maximum amount permissible such that the obligations of such
       Guarantor under this Note Guarantee will not constitute a fraudulent
       transfer or conveyance.

      3.       EXECUTION AND DELIVERY. The Guaranteeing Subsidiary agrees that
 the Note Guarantees shall remain in full force and effect notwithstanding any
 failure to endorse on each Note a notation of such Note Guarantee.

      4.       GUARANTEEING SUBSIDIARY MAY CONSOLIDATE, ETC. ON CERTAIN TERMS.

               (a)   The Guaranteeing Subsidiary may not consolidate with or
      merge with or into (whether or not such Guarantor is the surviving Person)
      another corporation, Person or entity whether or not affiliated with such
      Guarantor unless:

                    (i)   subject to Sections 10.04 and 10.05 of the Indenture,
               the Person formed by or surviving any such consolidation or
               merger (if other than a Guarantor or an Issuer) unconditionally
               assumes all the obligations of such Guarantor, pursuant to a
               supplemental indenture in form and substance reasonably
               satisfactory to the Trustee, under the Notes, the Indenture and
               the Note Guarantee on the terms set forth herein or therein; and

                   (ii)  immediately after giving effect to such transaction, no
               Default or Event of Default exists.

               (b)      In case of any such  consolidation,  merger,  sale or
      conveyance  and upon the assumption by the successor corporation,  by
      supplemental  indenture,  executed and delivered to the Trustee and
      satisfactory in form to the Trustee,  of the Note  Guarantee  endorsed
      upon the Notes and the due and punctual  performance of all of the
      covenants and  conditions of the  Indenture to be performed by the
      Guarantor, such successor corporation shall succeed to and be substituted
      for the Guarantor with the same effect as if it had been named herein as a
      Guarantor.  Such  successor  corporation  thereupon may cause to be signed
      any or all of the Note Guarantees to be endorsed upon all of the Notes
      issuable  hereunder which  theretofore  shall not have been signed by the
      Issuers and  delivered to the  Trustee.  All the Note  Guarantees  so
      issued shall in all  respects  have  the same  legal  rank and  benefit
      under  the  Indenture  as the Note  Guarantees theretofore  and thereafter
      issued in  accordance  with the terms of the Indenture as though all of
      such Note Guarantees had been issued at the date of the execution hereof.

               (c)   Except as set forth in Articles 4 and 5 and Section 11.06
      of Article 11 of the Indenture, and notwithstanding clauses (a) and (b)
      above, nothing contained in the Indenture or in any of the Notes shall
      prevent any consolidation or merger of a Guarantor with or into an Issuer
      or another Guarantor, or shall prevent any sale or conveyance of the
      property of a Guarantor as an entirety or substantially as an entirety
      to an Issuer or another Guarantor.

      5.    RELEASES.


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               (a)      In the event of a sale or other  disposition  of all
         of the  assets of any  Guarantor,  by way of  merger, consolidation or
         otherwise,  or a sale or other  disposition of all to the capital stock
         of any Guarantor,  in each  case to a Person  that is not  (either
         before or after  giving  effect  to such  transaction)  a Restricted
         Subsidiary of an Issuer, then such Guarantor (in the event of a sale or
         other disposition,  by  way of  merger,  consolidation  or  otherwise,
         of all of the  capital  stock  of such  Guarantor)  or the corporation
         acquiring the property (in the event of a sale or other disposition of
         all or  substantially all of the assets of such  Guarantor)  will be
         released  and  relieved of any  obligations  under its Note Guarantee;
         provided  that the Net Proceeds of such sale or other disposition  are
         applied in  accordance with the  applicable  provisions  of the
         Indenture,  including  without  limitation  Section  4.10 of the
         Indenture.  Upon  delivery  by the Issuers to the Trustee of an
         Officers'  Certificate  and an Opinion of  Counsel to the effect that
         such sale or other  disposition  was made by such Issuer in accordance
         with the provisions of the Indenture,  including  without  limitation
         Section 4.10 of the  Indenture,  the Trustee shall execute any
         documents  reasonably  required in order to evidence the release of
         any Guarantor  from its obligations under its Note Guarantee.

               (b)      Any Guarantor not released from its obligations under
         its Note Guarantee shall remain liable for the full amount of principal
         of an interest on the Notes and for the other obligations of any
         Guarantor under the Indenture as provided in Article II of the
         Indenture.

      6.       NO RECOURSE AGAINST OTHERS. No past, present or future director,
 officer, employee, incorporator, stockholder or agent of the Guaranteeing
 Subsidiary, as such, shall have any liability for any obligations of any Issuer
 or any Guaranteeing Subsidiary under the Notes, any Note Guarantees, the
 Indenture or this Supplemental Indenture or for any claim based on, in respect
 of, or by reason of, such obligations or their creation. Each Holder of the
 Notes accepting a Note waives and releases all such liability. The waiver and
 release are part of the consideration for issuance of the Notes. Such waiver
 may not be effective to waive liabilities under the federal securities laws
 and it is the view of the SEC that such a waiver is against public policy.

      7.       NEW YORK LAW TO GOVERN. THE INTERNAL LAW OF THE STATE OF NEW YORK
SHALL GOVERN AND BE USED TO CONSTRUE THIS SUPPLEMENTAL INDENTURE BUT WITHOUT
GIVING EFFECT TO APPLICABLE PRINCIPLES OF CONFLICTS OF LAW TO THE EXTENT THAT
THE APPLICATION OF THE LAWS OF ANOTHER JURISDICTION WOULD BE REQUIRED THEREBY.

      8.       COUNTERPARTS. The parties may sign any number of copies of this
Supplemental Indenture. Each signed copy shall be an original, but all of them
together represent the same agreement.

      9.       EFFECT OF HEADINGS. The Section headings herein are for
 convenience only and shall not affect the construction hereof.

      10.      THE TRUSTEE. The Trustee shall not be responsible in any manner
whatsoever for or in respect of the validity or sufficiency of this Supplemental
Indenture or for or in respect of the recitals contained herein, all of which
recitals are made solely by the Guaranteeing Subsidiary and the Issuers.


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         IN WITNESS WHEREOF, the parties hereto have caused this Supplemental
Indenture to be duly executed and attested, all as of the date first above
written.

         Dated:  April 2, 2004



                                    GUARANTEEING SUBSIDIARY
                                    -----------------------

                                    ISP MICROCAPS (U.S.) LLC

                                    By:   ISP TECHNOLOGIES INC,
                                          sole member


                                    By:   /s/  Neal E. Murphy
                                          -------------------
                                          Name: Neal E. Murphy
                                          Title:  Senior Vice President and
                                                  Chief Financial Officer


                                    ISSUERS
                                    -------

                                    ISP CHEMCO INC.
                                    ISP CHEMICALS INC.
                                    ISP MINERALS INC.
                                    ISP TECHNOLOGIES INC.



                                    By:  /s/ Neal E. Murphy
                                       --------------------
                                       Name:  Neal E. Murphy
                                       Title:    Senior Vice President and
                                                 Chief Financial Officer




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                                    EXISTING GUARANTORS
                                    -------------------

                                    BLUEHALL INCORPORATED
                                    VERONA INC.
                                    ISP ALGINATES INC.
                                    ISP MANAGEMENT COMPANY, INC.
                                    ISP REAL ESTATE COMPANY, INC.
                                    ISP FREETOWN FINE CHEMICALS INC.
                                    ISP INVESTMENTS INC.
                                    ISP GLOBAL TECHNOLOGIES INC.
                                    ISP INTERNATIONAL CORP.
                                    ISP (PUERTO RICO) INC.
                                    ISP ENVIRONMENTAL SERVICES INC.


                                    By:  /s/ Neal E. Murphy
                                        -------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer

                                    ISP MANAGEMENT LLC

                                    By:   ISP MANAGEMENT COMPANY, INC., sole
                                          member

                                    By:   /s/ Neal E. Murphy
                                        --------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer


                                    ISP MINERALS LLC

                                    By:   ISP MINERALS INC., sole member

                                    By:   /s/ Neal E. Murphy
                                        --------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer


                                    ISP TECHNOLOGIES LLC

                                    By:   ISP TECHNOLOGIES INC, sole member

                                    By:  /s/ Neal E. Murphy
                                        -------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer


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                                    ISP CHEMICALS LLC

                                    By:   ISP CHEMICALS INC, sole member

                                    By:   /s/ Neal E. Murphy
                                        --------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer


                                    ISP INVESTMENTS LLC

                                    By:   ISP INVESTMENTS INC, sole member

                                    By:   /s/ Neal E. Murphy
                                        --------------------
                                        Name:  Neal E. Murphy
                                        Title:   Senior Vice President and
                                                 Chief Financial Officer


                                    ISP GLOBAL TECHNOLOGIES LLC

                                    By:   ISP GLOBAL TECHNOLOGIES INC, sole
                                          member

                                    By:   /s/ Neal E. Murphy
                                         -------------------
                                         Name:  Neal E. Murphy
                                         Title:   Senior Vice President and
                                                  Chief Financial Officer


                                    TRUSTEE
                                    -------

                                    WILMINGTON TRUST COMPANY,
                                      as Trustee



                                    By:
                                        -----------------------
                                        Authorized Signatory


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